try viewing this website for the PIA DNS servers: https://helpdesk.privateinternetaccess.com/hc/en-us/articles/219460397-How-to-change-DNS-settings-in-Windows
then go to system > general. and add them there
THEN go to services > dhcp server > servers / DNS. add them there
post again after you have rebooted the pfsense router
i have found adding DNS to the general tab is what causes the leaks.. when i use the PIA DNS servers on the actual SERVER DNS it fixes leaks for me.
this is for PIA and AIRVPN… i also do not use the DNS forwarding tab. its disabled, i use the DNS resolver tab
not a pro, just sharing my experience with my setup