Device Reactivation

We have activated our Xfinity Streaming App on our Roku devices and works fine for months, except that for some reason, after a period of time, Xfinity app asks us to go thru the full device activation process again -   This has happend multiple times.  We have three Roku devices on differnet tvs and this reactivation process occurrs intermittingly on each of theses three devices.  Does anyone know why this would occur and what if anything we can do?

Thanks