iPhone compatibility changed

I was using xfinity mobile with an iPhone 8. I had some coverage issues at work so I decided to try another network -- but decided to switch back to xfinity mobile within a matter of a few days. I couldn't actually make the switch back though because the same phone that I was using with xfinity mobile literally 3 days ago, is now all of a sudden considered incompatible with xfinity mobile network. To switch back to xfinity mobile, now I would basically have to get a new phone.

Customer support representative I talked to had no explanation for it. They told me that "compatibility is determined by an algorithm", which is a non-answer that doesn't explain why a phone that was compatible 3 days ago would be incompatible now.

It doesn't make any sense to me, but I was wondering if:

1. this has happened to anybody else, or
2. anybody has any idea why this might happen? 

I considered the possibility that xfinity mobile now considers iPhone 8 too old but that doesn't seem to be the case. I checked my old iPhone SE (first generation, older generation than iPhone 8) IMEI, and that one is in fact compatible with xfinity mobile.