When you run the command on terminal:
/interface/lte/firmware-upgrade lte1 upgrade=yes
The modem will download the firmware and upon installing the lte will drop and that is normal... You should not do anything until the terminal informs you that the installation is done...
If for some reason it won't install it will indicate that it has failed...
After that the modem will automatically initialize again and get to Running status...
So, if you followed the above steps and you get a fail, let us know...
Also check here
https://help.mikrotik.com/docs/display/ ... areupgrade