Need to find fix - MR6150 just searching - no connection

This MR6150 is notoriously hard to connect.  I have been in the middle of several different large cities, with 5G coverage all over according to the coverage map - unit just searching with no connection.  Occasionally it will connect and later lose the connection, and then go searching for hours again as I travel through other 5G coverage areas.

At home now, and yesterday turned on the unit and it is searching away.  Left it overnight to charge battery, and in the morning it was connected to 5G.  Turned it off, then back on, and placed it on the desk.  An hour and 1/2 later it was still searching.

Then took the sim card (T-Mobile) and placed it in 3 other devices at the same spot on the desk:

    -  MR6500, instantly connected to 5G at 4 bars, 403 Mbps tested.

    - Inseego M3000, instantly connected to 5G at 3 bars, 245 Mbps.

    - GL.iNet Puli AX, instantly connected to 5G at at 4 bars 188 Mbps tested. 

This MR6150 has firmware 12.01.54, which is the supposedly the latest.

What can I do to get this unit working correctly?

Thanks,

Mark