Dear Eric,
thanks for this thread! Short story is: Never take gear to the mountain that you did not test down in the valley 
I updated the firmware of my MTR-5B-based GoBox station last week and did a few quick tests at home. Either uploading the firmware did not work correctly or the binary version 1.9 does not fit my hardware.
I tried for almost an hour to complete the activation, but almost nobody came back with a report for me. Initially, I thought that this was due to the very bad CONDX. But then I looked into Sotawatch and saw that @PA9CW (Tonnie) had posted a spot saying “Calling cq. But coming back with strangs dots and dashes.”.
Luckily, I had packed my TinySOTA (MTR-3B) as a backup and then changed rigs. This is why the problem was fixed after 13:38 UTC.
That was a close match - this was a 3-summit winter activation, and being left with a faulty rig on the first summit 4 days before the Winter bonus ends would have been quite a disappointment.
Will post an activation report shortly.
73 and again mni tnx!
Martin, DK3IT