I was once told, by someone who was involved in making this work, that most pools build 2 blocks in advance, by predicting which transactions are not going to be mined, and constantly update these predictive blocks

This mechanism was developed collaboratively in 2016, by several pools, and improved iteratively to reduce the incidence of invalid blocks

The issue with the delay at the start of mining a new block is not verification. It is ensuring that the candidate block does not contain any confirmed transactions. A pool can not build a candidate block from the mempool without removing the just-confirmed transactions from the mempool. But the pool can guess with a reasonably high certainty, by choosing lowest-fee-rate transactions for its initial candidate block

And then after 50 seconds or so, the pool replaces the initial block with a fee-optimized block

Jameson Lopp reviewed empty blocks a few years ago
https://blog.lopp.net/empty-bitcoin-blocks-full-mempool/

In that review, only ViaBTC was mining empty blocks, which implies all the other pools had implemented the next+2 mechanism
More recent observations indicate that other pools are now mining empty blocks

I read the GitHub comment about file corruption caused by deleting the wallet file from outside the app. I don't see how it fits this story. TAILS is amnesiac, all files are deleted on shutdown, so that bug could only affect a wallet created within a TAILS session. The workflow - create wallet, write seed phrase, copy & paste address to Windows Electrum, send transaction - would have to be fairly contorted to write the empty wallet's seed phrase and copy&paste the other wallet's address. Maybe I'm overthinking, and the out-of-app file deletion is exactly the contortion which would cause this

There is also his claim that he successfully restored the wallet with seed words in TAILS before installing the Appimage. I'm inclined to believe this. If it's true, then the file corruption problem is irrelevant, whether it occurred or not

I suggest the seed phrase he's using now is from a fresh wallet created with the 3.3.8 Appimage, an empty wallet. The seed words for accessing the coin in the older version Electrum wallet are somewhere else, or lost. This contradicts his claim that he has the right seed words. In the absence of proof and 19 months passage of time, it's more likely than any other guess, in my opinion

Some notes from memory ...

Around the time of this transaction, Electrum users were being phished using the (previously) built-in server-to-client messaging function. The initial response to this was to remove the messaging function. Some users didn't upgrade, continued to suffer from the phishing problem, so there was a decision to configure Electrum servers to refuse to connect to clients older than 3.3.4, to force users to upgrade

TAILS does not update very frequently, so there was a period where the Electrum built-in to TAILS was unable to connect to servers. Also, the Python source of the post 3.3.4 versions required a later Python version than available in TAILS. A "binary" Electrum package (Appimage) was built and made available, and then (at least in Reddit) it was repeatedly promoted as "How to run Electrum 3.3.8 in TAILS", with instructions

Eventually, a later TAILS update had the necessary versions of Python and Electrum

Welcome back
Many thanks

That's horrible bad news
You were the only source which included a full chainstate
The other person only has the Blockchain
Good luck restoring service

Web server currently offline

https://getbitcoinblockchain{dot}com
Failed to connect to getbitcoinblockchain{dot}com port 443: Connection refused

EDIT: Now getting an almost-empty HTML page