Hey there, I’ve had this problem for ever and can’t seem to find a fix. When I stream the same radio station to my mu-so and Atom the atom lags by about .25 of a second (estimated). Both systems are basically in the same room and on the same wifi. The only way I can play radio in sync is to first play on my atom and then multi room to my mu-so.
Also, when I stream from tidal to my Atom and try to multi room to my mu-so they are sometimes out of sync and sometimes not. It drives me bloody mad. 
Hi, if you play an internet radio station on different devices there is no guarantee that they will be in sync in the way that they would be on FM, for example.
Multiroom, on the other hand, should of course play in sync. There are occasional cases I’ve heard of where Naim multiroom goes out of sync. If you experience this you should tell Naim support so that they are aware and may be able to fix it.
I accept (begrudgingly so) that I shouldn’t expect streaming services to be in sync, but it would be nice if they were.
As far as getting out of sync while using multi room streaming from tidal I will try to bring this up with tech support. Sadly it mostly happens during the evening when beers and “medication” (yes, I have weed on prescription) have been consumed so it’s all a bit, well, you know, “difficult”. In the future I will try harder