I use Xfinity and have had no issues running PI-Hole for over a year. However, I do a few things that could make a difference - I have my own modem, not an Xfin

I use Xfinity and have had no issues running PI-Hole for over a year. However, I do a few things that could make a difference - I have my own modem, not an Xfinity rental. And I use better (and generally a more privacy focused) DNS (Quad 1, OpenDNS, and also Google DNS, yes aware that last is not very privacy friendly). Only problem is my Pi died and I haven't set up a new one, been considering setting up a Pi cluster so if one goes down I don't have to scramble to fix it for Internet to work in our house (although I can just update the DNS at my router until it's fixed, so not too bad).