@carlsbad2 My observation was when I had the Core on the slow side of my hybrid network, Ethernet + PowerLine adapters. Things worked fine for a long time even when I had the Core on the PowerLine side of the network. For example, I have ROON endpoints in my office, 2 bedrooms, family room, Livingroom, and garage. I had the Core in one of the bedrooms with a PowerLine connection to the network.
That worked fine until that George Harrison hi-res song. I was surprised that the stream would always stop at the start of the whistling. However, I was happy I had a reproducible event. After some testing I realized that putting the Core with a direct Ethernet connection to my Router which also has a switch attached to it solved the issue.
My router is in my office and I do not want any computer making noise in this audio centric room so I repurposed an old cable TV connection in the wall separating my office from a bedroom. I snaked an Ethernet cable to the bedroom from the office. This gave me a direct connection to the higher bandwidth of my network. After this the Core worked with all types of material.
My PowerLine gear is fairly old so maybe the new ones are better.
In my situation the Core today is on the Ethernet side and works with both the Ethernet side and PoweLine side.