Hi

If you are wi-fi less, it makes sense that Roon doesn't work on the iPad and iPhone. Is your PC wired to the network.

Is there any chance that you have a cable plugging back into a switch or router which is causing a loop. This can cause intermittent issues.
Is the PC able to access the internet when the zones drop? (sorry if you have answered some of these questions already).

Cheers
Tom

Main: G61SL, 218, HD621, 2*7200SE, 7200HCSE, M6s, DSW, Apple TV 4K, NUC (Roon server)
Secondary: Wiim Pro, 3200, Audio Core 200
F80