Couchbase Server won't start: Detected an attempt to offline upgrade from unsupported version

After a AWS node crash our Couchbase Server won’t start. The server logs show this message repeating

[ns_server:error,2021-05-06T21:22:22.832Z,ns_1@kup-couchbase-0.kup-couchbase-headless.couchbase.svc.cluster.local:ns_config<0.193.0>:ns_config_default:upgrade_config:391]Detected an attempt to offline upgrade from unsupported version {6,5,1}. Terminating.

We are running our own couchbase server build in containers, not using a managed Couchbase