Multidecrypt and shared files


I have issues with the server side encryption. Some users are ok, but new created users get the following error on shared files:
“message”:{“Exception”:“Sabre\DAV\Exception\ServiceUnavailable”,“Message”:“Encryption not ready: multikeydecrypt with share key failed:error:0407109F:rsa routines:RSA_padding_check_PKCS1_type_2:pkcs decoding error”

How can I fix it? Does anyone has a hint?
Is it possible to disable the server side encryption without loosing data and without removing all shares?

Have a nice day,