Same issue since I'll started tu use Teltonika in 2020! If you got a wrong firmware then you figur out still tis issue. I'm 1600 KM away from my house and in case connection is lost, I have to move onsite and to debug the issue (mainly a reebot helps but only for 24h). I'm using the RUTX09 with one carrier in order to remotely survey my house. The RUTX09 device is mounted within a QUMAX-Antenna. Furthermore RMS is also not working and this brings me to completely change the whole equipment to Zyxel (with Nebula) and it works very, very fine!!! In order to use Teltonika you have to be a Senior Professional Engineer in order to know which parameters affects what in which case (APN, Band-Type, etc).