I have experienced similar problems, with Pulse Flex 2i, Pulse 2i grouped with 2x KEF LSWII
Music was out of sync right from the beginning of playing a song, or ran out of sync after some time. Usually the sync was bad between KEF and bluesound, sometimes even all of them.
Writing back and forth with NAD support didn’t really give a solution, main concern on their side was to make sure that it can’t be their fault. Even if the error appeared month ago, after updating the firmware of the bluesound speakers.
Well, while writing to their support i started trying out a couple of things.
The setting that did the trick was the ‘Resync Delay’ in the Device Setup menu of Roon Software.
I set this to 1000ms (or higher) on each pair of bluesound speakers.
Since doing that i have never experienced a problem again. Thought i should share this.
Maybe you can give it a try too?
Cheers!
Torsten