Maybe this address is from that seed, however in a different derivation path. It is a legacy address, so we don't have to worry about segwit derivation paths. Maybe in a different account?

@AndreRoos, I would create a new wallet and try those derivation paths and insert that ismine("1YourAddressHere")

m/44'/0'/1'/0
m/44'/0'/2'/0
m/44'/0'/3'/0
....
I would try a few...

I think you didn't answer also what version of Electrum are you using on Tails. Is it 4.0? There is no 4.0, it is a phising.

Edit: I would also try one more thing.
Create a new wallet, insert your seed, click on Options and check "BIP39 Seed". Insert the ismine("1YourAddressHere").
Now do this:
Create a new wallet, insert your seed, click on Options and UNcheck "BIP39 Seed". Insert the ismine("1YourAddressHere").