The logs indicate very poor signal strength characteristics.
Are both antennas attached to the router?
Did you change the location of the router recently?
You can try using a different frequency band by changing settings in the WebUI Network -> Mobile section. Since your device uses band 20, other bands to try are LTE B3 and B7.
Another setting to change is APN value. Disable Auto APN in Network -> Interfaces by editing the mobile interface settings and set custom value according to your provider.