BUG with Set-ClusterLog -Size and the FailoverClustering_Diagnostic log
Trying to set the cluster log size via Set-ClusterLog will cause the FailoverClustering_Diagnostic event log maximum size to balloon to 18014398507384832KB. That is 18014 PB!
We have two separate Server 2019 Hyper-V Clusters that this affected. A MSFT employee on the Q&A site confirmed this also happened in her test environment.