Hey Guys,
I tried all of this. I Install Electrum from version 1.8.x to 1.9.8 and found out that the wallet was created with version 1.9.6 to 1.9.8.
From Version 1.9 to 1.9.x my Password works but the Seed-Box remain empty. In Version 1.9 I can successfully change the password but Electrum used the new Password to Encrypt the Seed a second time.
If i Change the password and dont set a new one, Electrum deleted the seed and change the wallet to Watch Only.
For now that is my Progress:
with a Pyhton Script i have decrypted the seed manually with the password (that one that opens the empty seed box) and got a huge "hex-seed" that i decrypt to a 48 word Old-Electrum Seed - but that is definitely not the right seed, i managed to short the "hex-seed" and convert it to a 12-Word-Electrum Seed - but it does not work either.
only for clarification, that is not my "real" wallet, i have found it with other Electrum, Multibit, Bitcoin-Core wallets that i used in the past. it have "only" 0.23BTC in it. My other wallets are safe on a Hardware-Wallet.
This is just about personal curiosity.
I found some resolved issues on Electrums Github - maybe they are to blame for my problem. I will keep you up to date. If anyone has other ideas I'd be glad to hear them.