So we have Dialed In on location and have been having problems with people connecting to the machine using the smartphone app. It worked for a while, then stopped. Over many visits to the location, I tried everything I could think of, including removing the BT from the USB dongle in the coin door area and reinstalling. Nothing. Eventually I came to the conclusion that the Linux BT driver was probably crashing, so I powered off and did a cold reboot. Viola! Problem solved - connects like a champ again.
I'm not sure how long it will work before it crashes again (and it WILL crash again), but now that I know what's happening, I can try to narrow down the circumstances of the BT driver crashing. Based on my experience with WoZ 6.xx (lockups) and Hobbit (sound popping), it will probably be related to having the machine on 24/7 with an unstable Ubuntu core.
Just thought I'd put this up for people trying to get it to work and failing. A cold reboot is the answer if it worked before and doesn't now.