Migration to hased storage fails due to encrypted attribute

Hi, I tried to migrate my projects to hashed storage on Gitlab 13.12.8 in order to migrate to v14. This however fails for most projects with the error:

“There is a problem with encrypted attributes: OpenSSL::Cipher::CipherError”

How can I resolve that / find out which attribute is encrypted / get rid of them? I tried rolling back, migrating again, reboots, everything. That read-only issue I stumbled upon as well I got resolved. But now I run out of ideas.

Thanks for any help.