Diagnostics/logs will give us further detail around the issue itself and the health of your environment.
cbcollect_info is a command line utility that provides us with detailed statistics for a specific node. Example usage:
C:\Program Files\Couchbase\Server\bin\cbcollect_info <node_name>.zip
Run cbcollect_info on all nodes in the cluster, and upload all of the resulting files to us.