This problem is very similar with
HBASE-13330. It is also a result of ServerShutdownHandler and AssignmentManager 'thought' the region will be assigned by each other, and left the region remain unassigned.
HBASE-13330 only dealed with RS_ZK_REGION_FAILED_OPEN in processRegionInTransition.
Region failed open may happen after processRegionInTransition. In my case, when master failover, it assigned all RIT regions, but some are failed to open(due to
HBASE-17264), AssignmentManager received the zk event, and skip to assign it(this region was opened on a failed server before and already in RIT before master failover). The SSH also skip to assign it because it was RIT on another RS.
Master recevied a zk event of RS_ZK_REGION_FAILED_OPEN and begin to handle it:
AssignmentManager skip to assign it because the region was on a failed server
SSH also skip it because it was RIT on another server