I ran into an issue where one instance in a cluster of application servers backed by HBase stopped processing requests. Looking at a thread dump, it seems HBase client threads are deadlocked:
The deadlock seemed to happen at the same time that a region server was abruptly stopped (the physical server was restarted unexpectedly).
I'm using the hbase async API. The hbase client version is 2.2.4. The server is running 2.2.4 as well.