Sonos over a mesh network is not advised, it never really works. I have a mesh network, and I solved this by plugging one of my speakers into the primary router and using sonosnet. Voila. 

I recommend you try that and if it works but you don’t want a speaker near the router then I’d look at getting a boost. 

edit: Just noticed you do have your amps hard wired into one of the Mesh AP’s . Again, I think you need to have something plugged into the primary router/DHCP handler.

Also, I think the move may work off the regular home WiFi and not Sonosnet so I am not 100% sure this will work. But - the entire stability of my Sonos network improved when I plugged in a speak to the primary router…. including my move. It just works now. 

I have considered swapping the 2 routers (making the downstairs router the primary which would then be hard wired to the Sonos amps).  I would have to deal with some IP assignment issues but not the end of the world.  The oddity is, for awhile the Moves worked fine in the current config (current firmware on both Sonos and routers).  I don’t mind going through the process of swapping the routers, but I’m not sure it will fix the problem.  Alternatively, I wonder if wiring the 2nd router to the primary via Ethernet (I would need to pull some lines) would solve the problem.  Somewhat defeats the purpose of having a mesh network if I have to connect them via Ethernet….  

I’m not sure a hardwire  would help. In theory it may, although I believe that many mesh system have a dedicated wireless backhall for node to node communication. So will a hardwire simply replace that  with little to no appreciable benefit? Or will it use a different networking protocol and fix all issues. No idea. I’d try plugging a speak into the current primary just to see if that helps. If it does then you can evaluate different options but I’d probably just give up and buy a boost!
 

 Then again my home ‘to do’ list is so long and I doubt my wife would let me prioritize my speakers! So a boost is a quick, effective and not terribly expensive in the grand Sonos scheme of things. 

*Or does the Boost only operate over Sonosnet?

iIt’s a thought.  And yes I’ve got a ton of other ‘honey-do’s myself.  One other thing to further complicate the matter.

I have the 2 Moves - and one Sonos Play 3.  The Play 3 has never dropped during playback - and it’s further away from the router than the Moves.  Makes me question if it’s native to just the Moves and if a Boost will solve their issues.  Guess I could buy one and send it back if it didn’t work

A Boost won't help. The Move definitely cannot connect to SonosNet.

How are they hardwired? Do both AMPs connect to their own ethernet jack on your mesh-node? 

All mesh-system I’ve seen uses RSTP which does have some incompatibilities with Sonos classic STP, so one idea to mitigate this issue would be to only wire one of the AMPs to the mesh, and daisy-chain the second AMP from the first AMP. 

But another idea might be that the Move is roaming between two different APs (mesh nodes). When that happens, maybe it has trouble continouing the playback. 

I have a hard time believing that primary/secondary node is the culprit here, the problem that arises with mesh-systems is if you would connect Sonos equipment to multiple mesh nodes, that would cause all kinds of weird problems.

Yes so the AMPs are daisy chained and connected to the mesh.  There are only two routers (the primary and the mesh) so if the Move(s) are indeed roaming it would be between one or the other.  And that could be the issue; the Moves are much closer to the mesh than the primary router so the signal would be stronger for the mesh...