I am running a Gen-1 system comprising two Connect ZP90's, a Connect Amp ZP120 and a ZoneBridge BR100. Intermittently, the two ZP90's keep dropping off of the (Sonos) system.  Checking my router web page, all components show up as connected and are assigned MAC addresses, even when NOT showing up on the Sonos app. 

One will disappear to be replaced by the other, before swapping again and (sometimes) temporarily all components will reappear on the system for a short time before disappearing again. This despite one of the ZP90's being hardwired to the router via a NETGEAR 8-Port Gigabit Ethernet Unmanaged Switch (GS108). Restarting the router seems to help temporarily, but isn’t providing a long term fix. Also, frequently, when trying to play a radio station on one of the ZP90's, I get a message saying "Cannot connect to Sonos Product" 

  I have sent diagnostics and the confirmation number is: 1656924348. Can  anybody help please? THANK YOU.