I guess it would also help to install some monitoring app like LTE Discovery and report observations. "LTE connectivity is bad" is too general statement. In my case (and I also reported it on Telegram channel):
I am in area where the Pro1x mostly uses LTE channels B3, B9 and B20. B9 and B20 are quite OK to signal level around -110dBm, but B3 is a disaster, even at level -85dBm.
Now the example problem is: In the area I have available B20 with -90dBm and B3 with -85dBm and of course Pro1x chooses the one with apparently stronger signal (B3). As a quick fix it would help to force modem