Did it happen even in your latest attempt?

Anyways, so the symptom's timing varies, interesting...
Are you sure that you're the only one who have access to your computer(s)?
Because it looks like someone has been creating the watch-only wallet by importing that address while you're away.
That's the only logical answer that I can think of.

I'm wondering, are you perhaps using "Deepfreeze" (wiki) or other similar software?

That's the correct pair, so it's working as intended.
IDK what that test is for though since the issue is about 'imported' wallet turning into 'imported - watching only' wallet.

That just proved that your Electrum is working as intended.
Pmalek also instruct you to check if the private key that you'll get from "1EHNa6Q4Jz2uvNExL497mE43ikXhwF6kZm" is the same as the private key that you've imported.
('1EH' is publicly known, no need to censor that address)

The shortcut is to open the 'Addresses' tab ("View->Show addresses" to enable the tab), the right-click on the address and select 'Private key'.

So you're abroad?
It may be the ISP, if the solution above didn't work, try to change your DNS.
e.g.: into google's (8.8.8.8), cloudflare's (1.1.1.1) public DNS or others.

There are a couple of online tutorials about 'how to change your network's DNS'.

The problem is Electrum is not a company or an entity, it's an open-source project that's being maintained by volunteers.

If you want to hear-out the developers currently working on the project, you can reach them in Electrum's repository in GitHub:
Repository - github.com/spesmilo/electrum | Contributors - github.com/spesmilo/electrum/graphs/contributors

That's a very famous topic that's been discussed quite frequently.

If you need more responses to that question, read these old threads:

• 2012: What happens when all bitcoins are mined?
• 2013: after all BTC has been mined, what then?
• 2019: How will Bitcoin survive after all 21M coins have been mined?

Any follow-ups or you'll just leave it unresolved?

If using a 'blockexplorer' doesn't concern you (privacy concerns), you can lookup that address and see if there's any unspent output(s).
If there's none, then it's indeed Bitcoin Core's issue when it scanned for wallet-related transactions.
e.g: blockstream.info (check if it has any "CONFIRMED UNSPENT" outputs).

It's also possible that the transaction that spent the funds wasn't mined and dropped from the mempools.
Better do a rescan to be sure.

Take note that you can't use the command above if your blockchain is pruned,
Go to your Bitcoin Core's 'Settings->Options...' and see if "Prune block storage to" checkbox is enabled.

Everything is in the software's code.
There's no "who", just the miners who compete for the winning blocks.
"when" is completely 'average', there's an ever-adjusting 'difficulty' that ensures that blocks can be mined in an average of 10minutes.
Each block's reward is currently 6.25BTC (+fees) which was 50BTC when Bitcoin was just released because it halves in every 210,000 blocks.

Pretty much everything covered in this 'the Bitcoin Wiki' article: en.bitcoin.it/wiki/Mining

Better than asking here in the forum where there's no official CMC representative.
Users will most likely answer with guesses and other non/related stuffs.

Bitcoin Wiki says, find a way to contact this guy: https://github.com/kallewoof
There's a Twitter link in his GitHub profile page and he's active there.

Try asking their support instead, there's an option for "Questions" on the number 12 in the list of request types.
Link: https://support.coinmarketcap.com/hc/en-us/requests/new

Unfortunately, there's no info in the 'Trending' page nor in their FAQs about the requirements for getting into the 'Trending Cryptocurrencies'.

Judging from the source code, it's supposed to be a Capcha that can't seem to load.

I don't know if it's legit but the stats that states: "642 months" to break even with your initial deposit is already a sign that it's not worth it.

Looks like someone has reported him, he's already auto-banned by a Mod, it's logged in the forum's deletion log: Archive: bitcointalk.org/modlog.php

A well-written single-address client will do that (send the change to the same address), but most wallets will use a "change address" for the remaining 0.5BTC.

I guess that API works like coinb.in which requires you to manually add a 'change address', or it'll use the remaining funds as fee.

Or instead of individual private keys, just save your "Backup Phrase", that alone can restore all of your prvKeys, including the new ones that you haven't generated yet.
You can get it from the 'Security' settings: "Secret Private Key Recovery Phrase".

Take note that it doesn't backup your Trading account.

There's no way you haven't seen this message at least once since it's configured to display in testnet mode:

(unless in the next sessions if the checkbox is ticked)

Read this TheBitcoinWiki article to know more about "testnet": en.bitcoin.it/wiki/Testnet

Does your computer contain your wallet backups like seed phrase or private keys? Or just the wallet?
Have you stored your wallet's backup online?
And which wallet, Bitcoin Core?

You need to rule-out every possibility of a "hack" and if there's no other way that it got compromised aside from physical access to your computer, then that's your primary suspect (the quoted message)

Or you could use your Bitcointalk account's signature space to promote your referral link, but that's only after you rank-up to "Jr. Member" (only as text).
It will be displayed below your every post.

Here are the requirements for the ranks and other info: Sticky Topic: Newbies - Read before posting
The forum rules including about referral links: Unofficial list of (official) Bitcointalk.org rules, guidelines, FAQ

Version 1.7 is available here (only from source): https://github.com/spesmilo/electrum/releases/tag/1.7
Version 1.8 and onwards' binaries are available in their archive download page: https://download.electrum.org/

Nothing in particular, specially the "copy the private keys" part.
After v3.3.3, there's been an option to prompt the user whenever there's a new version, but that's released in 2019.

Take note that seed phrase created with any other versions after v0.34 are still compatible with the latest version.
So importing it to those versions will do nothing but restore the same keys that would've been restored in the latest version.