Not sure there's really a thread for this specifically (though see all the 2.2.6 capability changes here: 2.2.6 capability update cheat sheet), but the setColorTemperature() command spefiication was updated in 2.2.6 to accept up to three parameters, with all but the first being optional, so something like setColorTemperature(Integer colorTemperature, Integer level=null, Number rampRate=null). If your driver only has the one-parameter version or didn't implement the new version correctly, that could be a problem (but in at least the first case would also throw an error in the log that would suggest this).
That being said, it's also possible the app is using the "old" way, a separate setColorTemperature() and setLevel() command (with only the CT specified in the former). In that case, many people seem to have bad luck with commands sent to Zigbee bulbs "too fast" in a row, apparently causing them to miss some. The "new" command might help with this if the bulbs are able to do this with a single "real" (Zigbee) message, which I believe is one of the reasons it was introduced. I haven't checked which command(s) Motion Lighting is really using, but if you have a custom app or rule you'd be able to know for sure. 
