I hate to sound like a broken record, but I'm in the same boat:
- Got my 12 Pro on launch day (10/23)
- Verizon
- Came with iOS 14.1
Thankfully my bf is in a number of group chats with me. Messages were being received in group chats (mixed and iPhone) inconsistently. Apple tried twice over chat, Verizon over chat twice and in person once. SIM has been replaced, resets of phone, network settings, you name it, so many times I lost count.
A Verizon Tier 2 Tech almost fixed it, bur 2 days later, back to random missing messages. Have an Apple appointment and plan to have them check hardware anyway (it won't be that, I know), but I have Apple tech in chat saying to replace my phone if it can't be fixed.
Not sure that will fix the issue (probably not), but this is infuriating. My brother got a 12 Pro and not sure if he's having the same issues we are.