I would be tempted to run a test with the 861, core and remote all being connected to the router (turn off all other network devices and restart the router).
The outcome should help to close down the problem. Here is a link to a long Cat 5 cable.

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