It seems it is a common issue that the couchbase client fails to reconnect to the cluster in the case of connect time out. See https://forums.couchbase.com/t/couchbase-java-client-not-reconnecting-after-connection-timeout/12583
We also experience the same issue. We had 20 app instances pointing to a 6-node couchbae cluster. We shutdown 1 couchbase node and started it after a few minutes. The KeyValueEndpoint connection is never reconstructed. We have to restart the apps to restore the connection.
We wonder why socket connection timeout is not treated for reconnect like connection refuse.