The only wallet that I know that's getting errors with OLD "Backup Phrase" (not SEED), showing "non-spendable" than "watch-only";
and requesting private keys in every send attempts than not displaying the send button... is:
Blockchain.com's (not a real) wallet.

I'm 70% sure that it's blockchain.info's (not ) wallet.
Luckily, they have a sublink that enables the users with old recovery backup phrase to restore into a new wallet.
Here it is: https://login.blockchain.com/wallet/forgot-password (the same link if you forget your password, but it accepts old seeds).