I have to wonder if there's some parts pairing issue going on with your phone. According to an internal Apple document I've seen, here is the list of paired parts on your phone.
Yes - Battery[br]
Yes - Display[br]
Yes - Camera[br]
No - Back Glass[br]
Yes - Phone Rear or Mid System
Now I fully admit I do not know what it means by "Phone Rear or Mid System", but generally when it talks about the back glass, it's including things like the charging coil and NFC antenna, so I don't think that should be affecting your phone; they didn't start pairing that until the iPhone 14 with its replaceable rear glass. Possibly on phones like yours without a removable back panel, that's what it's talking about?
Anyway, I don't have an answer for you, but just wanted to add this data point in case it sparks any ideas.