Xfinity app on roku will not function

Despite following all instructions to fix this problem, the xfinity app does not function on 2 of our 3 ROKU units. My internet signal is excellent, one of the problem tv's is hardwired to the xfinity modem. I can get much of what I want on FUBO and am about to get rid of xfinity tv, as it is too expensive to not work reliably. I can remove the app, reinstall it, restart roku and my tv as all instructions say and it will work for a couple of days and quit again. It is very frustrating.