- Someone somehow was able to put malware on my one month old computer, and somehow intervened the wallet creation process and modified the wallet before I encrypt it.
- Electrum has bug.
Maybe the seller put something on it?
Was the computer on offer from a corner shop somewhere that sells computers and electronics...
The bug thing is potentiallly likely.
I just had an idea, can you try going to the concole and type "getmasterprivate" and try importing that into a new electrum wallet. .