Automatic recovery of the failed postgresql master node is not working with pgpool II
It is as designed: when pgpool does the failover, the failed master is ejected from the pool so that there is a protection against a split-brain. If the failed master comes back again (degenrated master), pgpool will not automatically perform the recovery operation.  You have to manually execute the command pcp_recovery_node command.

If you want to automate this, then you can have a cron job running on each database, this cron would check the status of the database and when it detects a degenerated master it would execute the pcp_recovery_node command. This script can also take care of re-attaching failed standby databases (when a standby fails, pgpool ejects it from the pool and it does not re-attach it when the standby comes back).

I did something like that, it is a bit tricky, you must make sure that the script is never executed twice, for example if the cron interval is shorted than the time to perform the recovery (have a mechanism of a pid file to protect agains that). Otherwise it works.

As for repmgr, I use their scripts to perform failover, recovery, etc. but I don't use repmgrd to automate the failover, I found it safer to have the automatic failover done by pgpool.