If pihole becomes unresponsive, one reason may be that the diskspace is full. The diskspace may become full from an excessively large pihole database and or /var/log entries.  In a recent case, both were the cause.  Stopping the services and truncating the logs in /var/log and deleting the database worked in this case.  The following logs were large, but I elected to truncate/delete many others too.

/var/log/pihole.log
/var/log/pihole-FTL.log
/var/log/daemon.log