To confirm the issue, restore the same xPUB that you've used with the API to Electrum by selecting:
"Standard wallet->Use a master key" in the wallet creation window, increase the gap limit then, restart Electrum.
Note: It will create a watch-only wallet.

If it didn't restored the addresses created by the API, then it's their API's fault;
to check if it's your fault or someone changed it, check all of your bitcoin wallet's xPUB (Settings->Wallets and Addresses) if it's the same as the one you put in the API.

But if the balance is correct, then you might have selected an "archived" wallet in the "wallet's and addresses" from blockchain.com and used its xPUB key.
Because each of your accounts have different xPUB and should use a different derivation path when importing to another wallet,
Electrum will select the 1st account (default blockchain.com wallet) by default.

Or it's just another instance of their delayed client balance/status updates.

Question is: How many wallet names do you have in blockchain.com "Settings->Wallets and Addresses" and is there any marked as "archived"?

Cryptocurrency non-custodial wallets like Electrum doesn't work like a bank account.
It stores the private keys of your addresses that's used as the "key" to spend from the "recorded" data in the blockchain.
You're in full control of your funds including the security, Electrum developers or servers cannot intervene.

And that seed phrase contains all of those keys, it's never meant to be a "login info",
it's a "full backup" as stated in the warning from the wallet creation window (the image in my previous post #4).

It's hard to tell exactly how.

Maybe your Evernote's login info was compromised.
It could also be someone near that area since the transactions were made after you opened your wallet at that time.
...Or not, because if the connection is slow, it could take a minute to display the next/latest transaction(s).

Haven't heard of them, but it looks similar to chainalysis.com that investigates these cases.

This isn't secured since it's stored as non-encrypted plain text.
The seed phrase should be stored "physically" offline in a piece of paper.

You should've followed the instructions:

Although we can't rule out other possibilities, but I got a hunch that it's the seed that got hacked.

If a hacker can get his hands on your files, then he wouldn't be needing your Electrum wallet at all.
He can just import it to his own Electrum installation and spend your funds from there.

As far as the Electrum is concerned, it's the device where it was installed will decide if it's "easy to hack".
Plus the wallet type, 2FA and an "air-gap" set-up are pretty much "unhackable".

How about the wallet's seed, is it stored somewhere safe?
Can you tell which version of the wallet are you using and where did you downloaded it?

Those transactions were confirmed and cannot be reversed.
You can report it to the authorities as the only way to recover your coins is to find the culprit.

If that's the case, use dumpprivkey "address" command to export the wallet's private key(s).
The faster method, 'dumpwallet' wasn't available for that version.

Do you know which addresses have a balance?
If so, confirm it from a blockexplorer, then use that command in the console: 'Help->Show Debug Window->Click "console" tab'.
Example:If the wallet have a passphrase, enter this first before the dumpprivkey command:
(the commands requires the quotation marks, do not remove them)

Then copy the private key and import it to Electrum (electrum.org) using "Import Bitcoin addresses or private keys" option when creating a new wallet.

The second error was just a result of the first, so the issue is "signing" that might be cause by not having the correct private key of the used inputs.

Also, you need to be informed that your current balance isn't "final" because your client isn't synced yet,
although I highly doubt that version 0.8.5 will be able to sync.

What's keeping you from upgrading to the latest version?
You can backup the wallet and/or create a dump file if you're worried to lose your wallet if you upgrade to 0.19.0.1.

I didn't compiled the binaries, I directly installed and ran "run_electrum" through Python v3.8 with the pre-requisites.

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You can follow the guide in Github with some modifications.
1. Download Python 3.8 installer for Windows: https://www.python.org/downloads/release/python-380/.
2. Download Electrum from Github as ZIP, extract it (electrum-master) and paste inside python38 folder (for easy access).
3. Open a command prompt inside python38 folder (where python.exe was installed) using "Shift->Right Click->Open command window here".
4. In the console, enter these (requires internet):
To upgrade pip module to the latest version.
Probably pre-installed
Needs to be the same folder name as your extracted electrum-master.zip and including the slash "/" at the end.

5. To launch electrum, enter:
And wait for a few minutes for the first launch, a few seconds if it was launched before.

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You can create a .bat file with #5 to easily launch Electrum using double-click.
Create a new text file in python folder, paste the code from step 5, save; then rename the extension ".txt" into ".bat".
Create a shortcut of the bat file and name it "Electrum 4.0.0a0".

Hmm, not as most users described.
Even non-rooted device is as susceptible as rooted. As long as you've installed a malware, it will infect your system.

I'm sure that you've stumbled upon an App that can root your phone with a simple click;
So, a malware with that capability can easily flash, install something or alter some system level applications.

The added risk to a rooted phone is flashing custom ROMs that may have a more vulnerabilities than the stock Android.
And of course, more variety of risky "underground" applications.

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If you're installing a wallet, just make sure not to browse to shady sites and never install unnecessary app to your phone, like Facebook App

How do you usually shutdown Bitcoin-Qt?
Shutting down the PC while Core is running will corrupt the currently used datadir files.

If that corruption issue happens frequently, you may also consider scanning the disk for possible bad sectors.

I still have my old rooted android KitKat phone (local brand) with custom rom and as far as I know,
it has never been hacked due to the advanced permission management the "superuser" feature  have added.

But that's already covered by today's latest android version, like my current phone that i don't even bothered rooting.
Like the seemingly consensus here, latest phones doesn't need root access to be more secured, you'll likely get the opposite if you try.

For beginners, better off not tinkering with the things that they don't understand.

Mining is business, it needs to profit.
Anyone who's got a single S17 woudn't take chances to mine a block than a steady income from pools.
Unless they do it for research purposes, free energy lottery (OP) or JFF.

It takes a protocol level change to stop "pooling", it could never be persuaded.

Those "The Mempool" phrase from online articles and posts are usually the culprit why beginners are mislead into thinking that there's a central mempool in the network.
But that's the shortest way to tell "my/your node's mempool" so I can't blame them, "the" is a very general determiner anyways

There's no scam happened based from your replies, if it is a scam then the bitcoins shouldn't be sent to your watch-only in the first place.

You can create another Electrum wallet by clicking "File->New/Restore" and make an "imported wallet" using that private key that you believe where the address from your watch-only wallet came from.
When creating a wallet, select: 'Import Bitcoin addresses or private keys' then paste the private key (click "info" to know what to add based from the address type).

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-edit-
This sounds like an improvised scenario due to the inconsistencies (you're scammed, but received the funds), please clear this up.
Take note: Electrum developers don't have access to stored funds and wont be able to directly help recover lost funds.

He must be talking about the -i argument that specifies a text file with a list of prefixes.

If that's the case, bangbumbang is correct because
during my test, it didn't changed the queue once I've edited my text file while vanityseach is running.

The problem is that the coinbase transaction that he's trying to spend isn't the genesis block's.
He specifically set the block at height 4 to have a 1,000,000,000BTC reward and he's unable to spend it.

I can only suggest him to try it with 'regtest' first but I suppose he already did that.

You will receive the bitcoins regardless of the wallet's state because technically, bitcoins aren't really sent from wallet to wallet.
Anyways, Armory required a fully synced Bitcoin Core in order to operate. But crashes like that are often caused by corrupted database.

What is your Armory's version? 0.96.5?
You should paste the log (dbLog.txt and armorylog.txt) here and move this thread to Armory child-board for better assistance from the developer himself.

If it's restored as a watch-only wallet, then you've imported the address or master public key (xpub) to Electrum,
anyone can do that by getting a random address with balance from a blockexplorer and import it to Electrum

What you need to do is to restore the seed phrase (12-24 words) using the option: "Standard wallet->I already have a seed" and the options from my previous reply.
You can create more than one wallets in Electrum using "File->New/Restore" menu.
If you already done exactly that, then you might have got the wrong seed phrase since Electrum will restore both receiving and change addresses or it's out of reach of the "gap limit".

After importing the seed to Electrum, try to increase the Gap limit to 1000 or more by typing in the console tab (View->Show Console):
Then close the wallet and restart Electrum.
Also, check the other addresses in the address tab (View->Show Addresses) if you can see a familiar address.

The current wallet's unconfirmed transaction won't matter as it's only like that because the wallet isn't syced and wont be able to sync.
All you need is the seed phase of that wallet.

When importing to Electrum Desktop (not android), click "options" then, check "BIP39";
On the next window, select "legacy" then change the derivation path (below) into: m/0'
That includes the quotation mark. Then wait for the wallet to finish downloading the headers and sync (2-20minutes).

1. Maximum of 50 peers may not be an issue if you're connected across the globe and not concentrated to a single area.
(since that's quite the average incoming connections)
You can do that by setting multiple addnode=<nodeIP> from different locations, like different blockexplorer's nodes as they are connected to thousands.

2. Read the documentation about "Reducing traffic" (github-Bitcoin), it's indicated that maxuploadtarget only limits blocks older than 1 week, so your newly mined block(s) wont be affected by it.

Care to tell how low is your hashrate? "Lottery" is a relatively low number compared to the current difficulty.
Because if it's too low, your miner might take more than a year even when all the pools/farms stop mining Bitcoin.