I have found a problem with migration from 4.x motion sensor devices to 5.x motion sensor devices (the DNI was picking the wrong Hue ID to use at the end of the DNI after the last "/" character). For new upgrades, this is fixed in 5.1.1. For existing users, one fix is to restore a backup from 4.x and re-upgrade, although I realize at this point that this may not be practical for many. The other solution is to:
- Go to the Select Sensors page in the CoCoHue app
- Add any existing sensors as "new" sensors, as they should now show up in this list.
- Swap the device network ID (DNI) of the old and new devices.
- Remove the device from your hub that now has teh "old" DNI.
That is assuming you want an easy way to keep the sensors in any apps you might have already been using them in; another way is to simply add the devices like new (steps 1 and 2), then swap them out in all apps yourself, and remove the old devices after that.
If this is a problem for anyone (maybe you have a lot of sensors?), there would technically be a way to automate this with some option in the app, but I'm not sure how many people are affected by this enough to warrant that trouble. But this should avoid issues going forward. Sorry for the trouble, and thanks as always for the reports!
Oh, and CoCoHue 5.1.1 has been released with this change. 
