You've probably thought about this, but just in case:
The Pro1X has connection issues with LTE and GSM (calls). We do not know why, but we believe it is either: a problem in the hardware (yikes!) - or - a fault in the stock Android drivers and firmwares, which also SFOS is using. The latter (if existing) might be fixed in a future OTA from F(x)tec (that, eventually, also SFOS would pick up, I guess), but we do not know for sure.
There are many (many!) people reporting missed calls and general mobile connection issues in, both, stock Android and Lineage. I'm one of them, as you might