@markstanley
What are you using for the node?
Keep in mind the new back end observes the lora frame counters. The old back-end does not. So if your device resets between every frame it will have issues with the new back-end (at least until a new version of the back-end with recently merged patches is deployed)
Regarding the other devices, have you registered them for the same application as well? Would you mind posting (or PM) the output of 'ttnctl devices'?