This article is a solution to a problem I had.
If you are getting a lot of Mobile data disconnected or Joined 4G LTE or Joined 3G WCDMA messages in your log (Main Menu>Status>Network Events), you may find the following helpful.
In my case despite having 4 bars of signal strength (-61dbM) it turned out the issue was a poor quality signal.
If you take a look at the detail of your signal (Main menu> Status>Mobile) you will see three fields RSRP, RSRQ and SINR when you are on a 4G connection.
These were initially meaningless to me. After a bit of Googling the table at this link explains matters https://www.digi.com/support/knowledge-base/understanding-lte-signal-strength-values
I discovered my SINR value was very poor at -3dB. Bingo !
The solution was to purchase an external aerial. In my case a Poynting XPOL-1-5G (XPOL-0001-V2) .
This improved all the figures and solved my issue. I now have a stable 4G connection :-)
The moral of this is not to be taken in by the signal strength indicator. On its own it can be very misleading !