I don't think it would be the "file corruption bug"... as that would have required that you had (at least attempted to create) multiple wallets/seeds... and you seem very adamant that you did not have multiple seeds/wallets etc.
So, either you did have multiple wallets setup... in which case that makes things like using the wrong wallet possible, in addition to the "file corruption bug"... or you didn't have multiple wallets setup... in which case the file corruption bug is not possible.
Look, I don't quite remember now. I have this believe.....
Yes, might be, I did try to create & restore few wallets (for the purpose of finding solution) but if, then only
after I sent the test transaction to the lost walletHere is another thing as mantioned already few times:
- I sent first a test transaction to my "lost" wallet and remember seeing that incoming transaction onto my lost wallet - that is certain! Because.....
I remember seeing this transaction as 'Not Veriefied' all the time (until I lost the wallet)
So, I did the transaction and I saw it showing off in my wallet, even though as 'Not Verified', thus I understood it went through and eventually it will confirm.
That was the reason I sent the funds to the 2nd address in the wallet because for me it was clear it went through & eventually will be confirmed.
Following, many hours have past and nothing was confirmed, still as 'Not Veriefied", even though I put the mining fee for confirmation within 5 blocks (for big transaction within 2)
That is how I started looking for the solution: deleted the wallet files, recovered again, deleted again, restored again & so on.
Or am I misunderstanding and you're saying you restored the wallet once (prior to updating etc) and it showed the "lost" address, but not the transaction data?

Yes, correct! I idid restore the wallet twice. Did see the same addresses but didn't see the transactions.
That is why I had to delete the wallet anew (based on guide line on Tails website) & search for futher solution, where I came across the suggestion on Electrum website - to update the Electrum software manually - & so I did.
Since then I have never been able to restore the "lost" wallet with the funds.