WARNING!!! Aug 8, 2024 - Potential Flaws in G4AR 5G Gateway Firmware Update v1.00.09 Related to External Antenna Use

I don't know if your able to run the old TM Internet app with the G4AR or not, but if you can, there is a tab in there with "advanced metrics" that provides a lot more information than just "number of bars".  It would be interesting to see if the bands are changing around when you switch the antenna selection.  It may even be that you are changing cell towers completely.  If it's the later, you may be able to call T mobile and have them lock out the problematic tower.  It may be that the firmware update is just not playing well with your particular circumstances.  Advanced metrics may shed some light on it.