The verdict is fine since there's no way to produce a reproducible build for the android version (latest post of the issue).

They also got a point when they mentioned that the google play version is different from the development build that they successfully compiled
since Electrum Devs are working on the "master branch" rather than a development branch, the source at that point has a few/lot of commits ahead from the google play version.

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Okay, this is the last of Electrum-specific discussion for me here.

This approximation of the common inputs looks close enough: https://bitcoin.stackexchange.com/a/87276
That's if you don't need the actual numbers, otherwise getting SegWit inputs' virtual size will be complicated (example).

Aside from the post above, there's another inconsistency on that site:

It was published on 2019 Dec 11:
But it said that the latest version is v4.0.4.0:
FYI, electrum v4.0.4 (not v4.0.4.0) was only released on 2020-October-15.

I wouldn't trust that page if I were you since they can't differentiate fake electrum and the original.
Update: I have read the whole article and it looks like that the version written in the page was updated somehow but other links like readme.md aren't.
The date and version are still misleading.

Coinbox seems to be using a different "derivation path" than Electrum's default.
I've tried various paths but nothing restored the first '3' nor 'bc1' address of coinbox.

I'll try some other variations and update you later if I've found the correct one.
For now, if it has balance, try using "Detect Existing Accounts" in the 'Script type and Derivation path' selection window of Electrum during wallet restore session.

There's a simpler way to send transactions without going through the "advanced preview".
You just have to disable "Advanced preview" in the settings: "Tools->Preferences->'Transactions' tab".

That way, it'll be signed and broadcast automatically after you click "send" under the "confirm transaction" dialogue box when you clicked "send" in the send tab.
But if you want to open the advanced preview, you can click "Advanced" in the same dialogue box.

It will get rejected due to another reason: "too high fees". That includes blockcypher.
He needs the one with the normal fee.

That will defeat the purpose of using a hardware wallet since you've already typed your seed phrase on an online machine.
If you really need to, just do it on an Air-gap computer; if you want to see the balance, get the "master public key" from the wallet information and create a watch-only wallet on an online machine.
You can easily compare the addresses by opening the address tab (View->Show Addresses).

You don't have to guess which wallet type, you just have to check any address with balance from your ledger and check the first character.
If it starts with '1' - select legacy; if '3' - p2sh-segwit; if bc1 - native-segwit.

May I?
No they won't, sent bitcoins are irreversible once the transaction was confirmed (yours currently has 251 confirmations).
If you have posted earlier when you've just sent the txn, there may be a chance.

This is useful when you accidentally sent to the wrong address again:
Since you're using Electrum, I'd suggest you to upgrade to the latest version 4.0.4 from the official site (and verify the file's signature).
That version has an option to "cancel (double-spend)" an unconfirmed transaction if it's marked as rbf (default: on).

Yes,
Since 150+ nodes are still accepting it, there's a 'very very slim' chance that it will get into a mining nodes' mempool (that also accepts such transactions).
But re-broadcasting it after getting dropped isn't worth it, IMO.

The "unknown" miners must be inaccurate and may be another one of those known pools, but the named ones could be reliable.

blockchaindotcom, the one I suggested to use, is basing it on the coinbase transaction's address.
You can click the miner's name and you'll be redirected to an address' transaction history.
That suggests that they have a database of addresses linked to mining pools (there may be two or more addresses linked to a single pool).

Depending on the fee rate of those transactions, but I bet that was the case.

There's also a chance that the service is legit but those transaction were mined by pools first since their fees are actually good enough and pools' hashrates are higher.
If you can gather more transactions, that should give you a more accurate conclusion.
There was a case when "some accelerator" took all the glory with a "done" quote while I'm the one who did the work.

Some of your previous posts suggests that you're using Electrum.
And the "pending" in electrum's receive tab is just an "invoice", you're not actually in the process of receiving bitcoins.
Check the 'history' tab first and look for the latest transactions, you may be looking at an outdated/different invoice for a different address on the receive tab.

If there's no similar inbound txn, contact the sender since he clearly didn't sent any or it was dropped from all bitcoin nodes' mempools.

Here is a very easy way to tell if they are really accelerating your transaction:
Upon getting a confirmation,  use a blockexplorer (specifically, blockchain.com) to check the block height of your transaction
and there's usually a pool name (set by the blockexplorer).

If it's "unknown", there's a good chance that the person is solo mining to include the accepted transactions.
If you'll only seeing random pools, then it's a rip-off, or the fee is just enough to be mined within the next few blocks.

For example, ViaBTC accelerator when used will be displayed as the miner of the accelerated transactions.
I've used it trice during this "high fee season" and the results are consistent.

Maybe you're using ETA, which I believe is "remaining time", during times like this, it will suggest a very high fee.
You can choose "Mempool", it usually suggests a cheaper fee than the above, set it to "1mb from tip" for a fair transaction speed.
But it will still depend on other factors like how fast blocks are being mined and the number of transaction added to the network.

Static is just a slider with fixed amount of fee rate, it's not based on anything.
Good for setting your desired fee if you do not want to open the advanced preview.

Take note that it was removed in v4.0+ and it's integrated in the "advanced preview" which can be accessed by clicking "advance" in the send window.
He can also set to automatically use advance preview after clicking send in the settings: "Tools->Preferences->'Transactions' tab->Advanced Preview".

It's not the address, the one that should be re-spent is the same UTXO that was spent by the to-be-replaced transaction.
You should first check both transactions in the console (Window->Console) using getrawtransaction, eg:
Look for the inputs ("vin"), if at least one of them has exactly the same "txid" and "vout" (under the txid) as the other one's (I think they aren't).

-reindex may not be useful in this case.

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BTW, -zapwallettxes shouldn't be used in the console, you should launch bitcoin core with it.

You'll have to re-download and verify all blocks if you use -reindex because it's a pruned node.
and 'abandon transaction' will only be available if the transaction isn't in your mempool.

Since it's marked as RBF, as a workaround you can manually create a transaction that spends the same input(s) which sends the funds back to your own wallet.
Here's how to create using the console/bitcoin-cli: createrawtransaction | signrawtransactionwithwallet | sendrawtransaction
But if you're fine with the current outputs, just let it be, it'll be confirmed later or dropped after 2weeks approx.

But what's the deal with the thread's title.
Did you double-spent one of the transactions? Because if it was double-spent, it should be out of your mempool by now.

Try to launch Bitcoin-qt with -wallet='directory' argument.
That will instruct it to use the wallet.dat in that directory (although it should create one in the data dir by default).

If it didn't work, tell us how bitcoin core was installed in your RPi.

470mb for 13 hours isn't bad, you might also need to reduce the number of connections in order to save some upload bandwidth.

Read this to find more options to reduce traffic: https://github.com/bitcoin/bitcoin/blob/master/doc/reduce-traffic.md
Info for -maxuploadtarget is included in that list with the reason why it reached higher than your set value:

Hmm, since this is the same as the PM, I take that this is a reply to my post on the previous page.

Double-check the transaction again, because they usually have a "change" which certainly belongs to your wallet.
Double-click the txn in the history tab and look at the "outputs".

If there's only one output which is your own change addr, then you have likely copied your own address or used cancel transaction unintentionally.
Note: "Cancel transaction" will double-spend the transaction's input(s) and send it to one of your change address.
In this case, there's nothing sent so there's nothing to recover but there'll be a deduction from your balance which is that transaction's transaction fee.

But if there's another output, then check if it's the same as the receiver's address and look for "Replace by fee" at the upper right.
If it's "true", then you should be able to use "cancel transaction" in case you want to cancel it, which is only available for v4.0.4.

Mathematically?
If it's fiat balance, you can enable it in the settings: "Tools->Preferences->'Fiat' tab" - Select "USD" under "Fiat Currency".
Wait for a few minutes and/or restart Electrum to connect to the source's API.

You may have to play with the "Source" because some of them didn't work at my end.
Mine is set to CoinDesk.

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If it's the Android version, the setting is in: "Menu (...)->Settings->Fiat Currency".