I am on my 4th Oneplus 8 pro handset. I got one about 6 weeks ago and it worked perfectly in every way until I dropped and lost in in deep water.  My insurance company insisted on a parallel import version (model IN2020 rather than the IN2023 originally) from a different retailer. That handset seldom connected to mobile data networks (on Spark) although always seemed to retain a phone/sms link ok. A replacement IN2020 from the second retailer did not work either. So they advised the insurer that they could supply a suitable replacement. ( BTW the IN2020's were clearly labelled for sale in mainland China only and did not have a fast charger)

I now have a replacement IN2023 from the original retailer and it has been generally fine for most of the week but now won't connect to mobile data. (my wife's iphone does fine so I don't think its a network problem).

i have tried all manner of reboots, forcing no 5g or 4 g connections, swapping the SIM between trays and nothing has worked.

I would appreciate any insights or suggestions people may have. thanks.