Weird. I've had a Pi-Hole + Unbound running on a Pi Zero since 2018 and it's never had any issues. I expected the Zero to kinda suck but it has been nothing but smooth sailing. It gets USB power from my router and even if my router reboots the Pi also auto reboots itself.
I do next to no maintenance on it and it just keeps on chugging along. Maybe once every six months or so I SSH in and do a pihole -up and that's it.