iPhone alternates between SOS and full bars, data unusable

My phone keeps switching between SOS mode and full signal bars. Even when it shows full bars, my cellular data doesn’t work. I’m on a family plan, and none of the other devices are experiencing this issue. I’ve already factory reset my phone, activated a new eSIM, and tried toggling airplane mode, but nothing has worked. I also contacted my carrier, but they couldn’t resolve the issue—they said everything looks fine on their end.

I’m not sure if this is relevant, but when I run diagnostics on my phone, it occasionally reports a hardware issue—though the results are inconsistent.

[Re-Titled by Moderator]