Is it possible the seller blacklisted the phone recently, and only Telus updated the IMEI in their database so far?
If you start losing the ability to use it on all operators, you may be a victim of a scam. I would go to an Apple Store right away and get it sorted out.
is it possible its been locked out of the telus network ? Lol....like the opposite of being locked to a network? Is this even possible? @sheytoon do you know anything on this subject?
What you allude to is the whitelisting of IMEIs before a device can register onto the network with a particular SIM. As far as I know, no Canadian carrier has ever had a requirement for devices to be "white-listed" before they can be used. This is something that Verizon (and possibly Sprint) does (IMEI must be recognized/certified to work on their network before it's allowed to register onto it with a Verizon SIM).
Update... my Bell SIM no longer works in this iPhone XR. I haven't re-tested the Rogers SIM yet, but this leads me to think their is something physically wrong with the phone.
I tried a Koodoo SIM today with no luck. I'm going to re-try a Rogers SIM again for entertainment purposes, but I think my next stop is to the Apple store to see if they can confirm if their is a hardware issue related to the cell/network part of the phone.
Your assessment is very reasonable, based on your update (as are suggestions about it being black-listed, which are plausible). If it's not black-listed, then it sounds like maybe an intermittent issue with the radio (hopefully not), or antenna connection (a bit easier to overcome, if it's a popped connector for example).
The ability to connect on Rogers might suggest a stronger signal or tower in closer proximity (compared to Telus tower), so that even with impaired antenna, it's connecting. But, without details, that's just speculation.