I can export my altcoin and bank accounts from Bitsquare without problems. But if I want to imort them into Bisq the files disappear from the file system and nothing happens.
what can be the reason?
Yep, the new version is not backward compatible, you’ll need to re-configure your accounts…
Welcome to the new bisq 
The data is not compatible. You need to setup accounts manually. Btc funds need to be sent with a tx, as wallet is different format (BIP 44).