Dougga Hi! Sorry, the notification got lost in the inbox
I'm pretty certain this was a hardware issue. I've returned my phone and got a replacement and it worked perfectly.
I measured packet loss by simply pinging different IPs (mostly 8.8.8.8), I know it's a bad diagnostic tool, but the phone was objectively just extremely unstable and borderline unusable over cellular data.
The phone I got as a replacement has worked flawlessly ever since I got it after returning my original purchase back in February or early March (I don't remember exactly)