Maybe, but I suspect it's working like this:
- Pi boots then requests locally configured IP from DHCP server
- DHCP server grants 30 day lease for requested IP
- Pihole runs fine for awhile, DNS requests are properly handled
- IP lease expires, DHCP server returns IP to available address pool but doesn't reassign it to anything yet
- time passes
- Random wireless device connects to router, DHCP server assigns IP to new device
- DNS requests to Pihole fail because the IP was assigned to the recently connected wireless device
This would explain why Pihole appears to cause problems every month, sometimes a little longer.