Just for diagnostic purposes what happens when you change back dnsmasq to port 53. If you do this pihole should be up and running still. Then try disconnecting and reconnecting a device.
Also for clarification what do you mean by "The DNS isn't working anymore on that device"
I'm going to try that later today.
The DNS lookup isn't working.
Question: Is it a problem that the pi-hole ip is the same as the router ip?