Part of the terrific service Freefly is doing for ALTA owners has resulted in them sending back ALTAs with the SYNAPSE set back to its factory configuration. Unfortunately, when I got mine I couldn't get my ALTA to arm, and it was because the Futaba's channel 9 (the arm disable switch) wasn't set up anymore. Adam from Freefly support walked me through opening the bay between booms 4 & 5 to expose the configuration jumper, which has to be removed to change channel assignments in the app. Once we did that it was simple to re-assign that switch to channel 9 and everything works properly now. This is documented in the manual if you need step-by-step instructions. Please note that the new app and firmware do slightly change the behavior of this switch, so you'll want to take some time to familiarize yourself with the new way of doing things. Whew!
Thanks for posting this Steve - just received mine back after some repair and I noticed this issue - I suspected the jumper was preventing the setting change, but glad to see it confirmed.
I just noticed however, that according to the manual, it's between booms 5 & 6 (see the attached image).
Same thing happened to me. It took me a little longer than I'd like to admit before remembering I had to remove the jumper in order to re-assign the channels. I'm sure this will help at least a few people down the road...