Do you run your PiHole on top of Docker? There's an issue with docker and Raspberry Pis which makes the network crap out periodically. So if your PuHole becomes unavailable until you restart your Pi it might be this:
https://github.com/raspberrypi/linux/issues/4092/
Solution is to add "denyinterfaces veth*" to the dhcpd.conf
Do you run your PiHole on top of Docker? There's an issue with docker and Raspberry Pis which makes the network crap out periodically. So if your PuHole becomes unavailable until you restart your Pi it might be this:
https://github.com/raspberrypi/linux/issues/4092/
Solution is to add "denyinterfaces veth*" to the dhcpd.conf