Whenever I try to use the multi room feature I always get drop-outs on one or more of the streamers. Typically it will be starting multi room from the main system to the QB2 in the kitchen. Main streamer is a NSC 222 but this behaviour was also present when it was an ND5XS2. All devices are connected by WiFi, wired really isn’t an option. We have a mesh WiFi system using BT Whole Home WiFi discs. The main streamer is in the same room as the router and master disc, the Qb2 in the kitchen is right next to a disc in the kitchen. Internet service to the router is 500Mb and the worst speeds I see on WiFi are still in the 100Mb ball park depending on where I am in the house. So how does the QB2 synchronise with the NSC 222? Does it create its own private WiFi network or is it a case of two separate but synchronised streams or what? Even hi-res audio doesn’t require that much bandwidth so I’m puzzled as to why I keep getting these drop outs. I can stream concurrently to both units with no issues so I’m guessing there is something about how multi room functionality is implemented
Multiroom uses your regular home network to stream from whichever device you choose as ‘server’ to the client streamers. Bandwidth shouldn’t be a problem, especially if you are only using a small multiroom group. I would guess that there is some other connectivity issue on your home network.
As a test, what happens if you use Apple Airplay or Chromecast multiroom? These do it independently of Naim’s multiroom so might give you some pointers as to where the problem lies.
I don’t use multi room at present but I did notice, in a similar set up to yours, that drop outs occurred frequently when using the ND555 as the “host” and the QB2 as the “client”. When using the QB2 as the host , the dropouts disappeared.
I don’t know why this happened but it was a fairly consistent issue.
That probably doesn’t help much, but at least you know you are not alone! 
I have an Atom and gen 1 Muso and QB all on wifi (Muso wired the the mesh unit). I’ve always struggled to use multiroom due to drop-outs. It quire often works for a while and then starts playing up, don’t think it matters which unit I use as the server. Currently I’m using EE for my Internet and prior to that BT (I know same company). Seemed to have the same issues with either router, however there may be a slight improvement with the EE router but due to the drop-outs I seldom try using it now. I know this doesn’t help but at least you’re not on your own.
Mesh is the work of the devil, or at least it is to me. We tried three different systems and none worked reliably. We now have a really powerful Netgear Nighthawk. We have an Atom HE and three Qb2s. All four Naims are wired to the EE 8 switch. Multiroom works faultlessly. All the boxes connect and any can be used as the master. Sorry to be dull!!
We live in a large-ish house with a weird layout and solid walls everywhere and I don’t think even the most powerful router would cover the whole house so a mesh system is the only thing that works. Even with a mesh system due to the layout and walls some parts of the house are just about 100Mb from the 500Mb coming in to the router. Ethernet to the 3 Naims would be a major rewiring job so WiFi it is for now. At least is seems my multi room issues aren’t unique. I’ll try @ChrisSU‘s suggestion again, first time I had a look the Google home app couldn’t find any of my devices but that may just be down to operator error as I’ve never used Google Home app before
How is your mesh setup configured? A properly set up mesh network should be rock solid, and problems are often caused by basic setup issues such as trying to run a DHCP server on more than one device.