Resolution:
The following messages are seen in the log file of the standby server:

Missing heartbeats from primary server 'tcp://p:7222'.
Server activating on failure of 'tcp://p:7222'.
Server rereading configuration.
Recovering state, please wait.
ERROR: Unable to open store file '/shared/sync-msgs.db', file may be locked.
ERROR: Unable to open store file '/shared/async-msgs.db', file may be locked.
ERROR: Unable to open store file '/shared/meta.db', file may be locked.
ERROR: Server failed to recover state.
Server is re-entering standby mode.

When EMS FT is configured, the primary server regularly sends heartbeats to a standby server (ft_heartbeat in tibemsd.conf).  If the standby server does not detect the heartbeats from the primary server within ft_active (tibemsd.conf), for example, due to a temporary network issue, the standby server will try to acquire the lock on the shared storage. As the primary server is still running and holding the lock (exclusive lock), the standby server is not able to obtain the lock. The standby server prints, "Server failed to recover state" and re-enters standby mode.