Last time I ran into a similar issue I was testing upgrading from a really old version (bitwardenrs/server:1.10) to the newest version (vaultwarden/server:testing) and I noticed that I had to delete all the data/rsa_key.* files. Have not looked into the why.
But if you are using multiple vaultwarden instances make sure that they have the same rsa_keys (I think there are some existing threads with more information.)