The Hbase Masters can be stuck on a Standby state if it is still recovering the lease on the MasterprocWALs. You can check the same by looking at the restart logs of the Hbase Masters.
Check: hdfs dfs -ls -R /apps/hbase/data/MasterProcWALs > Check How Many Files (10000)
Possible Solution: Sideline MasterProcWALs + Waiting On RecoverLease