^This.
@OP:
What kind of addresses did electrum produce the first time? Did they start with a 1.. (legacy) ?
You might try to open the console (View -> Show console -> Console tab) and enter this command:
ismine("YOUR_ADDRESS_HERE")
It will return true if this address is part of the wallet.
If it does return false and you are sure your seed is correct, then most probably the derivation path is wrong.
You can choose the derivation path when restoring from a seed and clicking on 'options', choose BIP39, and edit the derivation path in the next window.