Chosen Solution
This phone has been previously liquid damaged and cleaned very well on the logic board. Now the leftover issue is: Service Provider option in settings keeps appearing and dissapearing, phone sim card detect fine, goes searching then no service. IMEI and modem firmware displayed in settings, checked #06 no problem there too. Is it okay to reflow the U_WTR_RF transceiver chip because of liquid damage before? Maybe it’ll fix the problem?
If the IMEI is showing, then the problem is not the usual long-jumper Baseband repair. You could try to reflow U_WTR_RF but I would probably reball it instead. You could also look at U_ASM_RF & U_WFR_RF. @teetopp summarizes it well in this answer (Service is “Searching” indefinitely).
