Number Changed to Primary error?

I have a pair of friends who each have new iPhone Xrs. When they try to text each other, sometimes it works and sometimes they get the message "Number Changed to Primary" and the message shows as sent by SMS, but never actually gets there. In addition, when one of them, call him A, tries to call the other, B, it rolls directly to voice mail. But B can call A without any issue. It's always A with the issue, never B, at least so far. We found an article about it (https://ios.gadgethacks.com/how-to/fix-number-changed-primary-bug-iphone-xs-xs-max-0189183/) that said to reset iMessage and FaceTime, or do a soft reset of the iPhone or do a hard reset, restore. None of that changes the behavior of the phone. Once the "number changed" appears, Message fails from all the iDevices associated with the iPhone, and phone calls via an iPad fail as well.

Anybody got any hints on what might be wrong here? At this point about all I can suggest is to take both back to Apple and see what the Geniuses have to say. A quick internet search did disclose that there are other folks showing the same issue, but none of them seemed to have any answer other than reset, reset, reset.

Sounds like these iPhone Xrs have dual SIMs in them, the regular kind and e-SIM and for some reason the connection to the Apple Servers (for iMessages) was made through the secondary SIM interface and that must have failed or whatever and it switched to what is marked as the primary interface. This switch might or might work. If the phones have dual SIMs and they aren't provisioned appropriately, I'm guessing goofiness with ensue.

Beyond just resetting, can you go to Settings->Messages and then for iMessage and Facetime Line, you should choose the number you want to default to.

If these phones do not have dual SIMs, then you shouldn't be seeing any of these issues.

For reference: https://appletoolbox.com/2018/09/seeing-message-number-changed-to-primary-on-iphone-xs-or-xr/

Yes, they have dual sims, and I just found the same article, Ashwin. But I don't think the eSim is set up, he just has a regular SIM in right now. I ran my XS that way for a long time, just shifted my Verizon to the eSIM in anticipation of traveling and using a second SIM in the UK, and I've never seen the issue. But I'll pass your suggestion along to him, thanks.

I wonder if having the eSIM but not setting default number might be confusing things? I would think not have the eSIM setup should make the phone work like it only has a single number, but I don't have any practical experience with this to rely on.

Yep, I had the same thought just now. He's with T-Mobile, so I suggested he take the iPhone to a T-Mobile store, get them to move the SIM to the eSIM and remove the SIM card altogether. I've done that with my Verizon SIM. Then you set the eSIM as primary. Normally, and before I had Verizon moved to eSIM, it works, and did work, as if it were a single-sim card. But I'm wondering if just the presence of the eSIM is triggering the issue, which might be resolved by making the eSIM the ONLY Sim. I've sent him the suggestion.

Are they using separate Apple ID's? Are their phone numbers, and emails associated in the Messages app?

Separate AppleIDs, Messages and phone worked until each got a new iPhone. Same phone numbers and emails, no change in Messages. I'm pretty much stumped on this one.