SQL Cluster failover doesn't work after applying SQL Server 2016 Service Pack 2
Actually, it looks like storage issue. I would recommend you check S2D storage. This and this might help you.
Assuming you already run SQL Cluster on top of S2D, what is the number of nodes? 


If it is a 2-node S2D cluster, I suggest you consider to move to AlwaysOn Availability Groups where is no need in shared storage or Failover Cluster Instances but on top of StarWind VSAN Free. AlwaysOn Availability Groups provides you with active-passive application level replication. StarWind will do active-active block-level replication featuring SQL instance failover between nodes.