I'm finding that a member cannot Leave() the cluster if the status is MemberStatus.Joining. It is only allowed to leave if it is MemberStatus.Up.

https://github.com/akkadotnet/akka.net/blob/dev/src/core/Akka.Cluster/ClusterDaemon.cs#L1195
if you call Leave() when status is Joining, the member is considered unreachable by the cluster indefinitely.