I am having the same issue. I came to post this exact same question. I was having issues with the GPS on one of the units and saw the other thread about flashing to 1.2.65.0adc5ce and that cleared up the GPS issue on one of the units.
They were both originally flashed to 1.2.64 and were unable to see or talk to each other. Flashing to 1.2.65 made them both visible to each other but they are not passing messages and ironically the unit that the GPS was working on no longer works. Fixed the other unit though.
Ok, this is what I did to fix both issues. To clear the GPS error I went outside and hit the reset button. It came up. For whatever reason the GPS on that particular unit does not work inside.
To fix the message issue I reset the other unit as well. Messages go through now. I am not sure exactly why it worked but it worked. Hopefully someone more knowledgeable than me comes in with a better response but give that a shot
this is an antenna that works well on my Tbeam’s. https://www.aliexpress.com/item/32661973474.html
It is an active antenna with much gain and the current (only a few milliAmps) is delivered by the u-blox module, which by default is configured to feed an active antenna.
Thanks for that product. I had a few larger active antennas laying around but they are not well matched to whatever the ublox is expecting (long coax).
My included little antennas have been working reasonably well for me, even indoors.
Replacing the stock 915mhz antenna is the first priority, but for a buck a piece… can’t go wrong there!