I restarted a worker from the leader through the UI, but it’s not showing back up in the workers list.
There is a chance that the permission on your Cribl Home folder may have changed. If you are running Cribl as as the user Cribl, ssh to the problematic worker, and try running
chown -R cribl:cribl /opt/cribl. Once you have done this, run
systemctl start cribl.