Steve, you’re an expert! Posted this on the Roon forum and drew blanks… degenerated into a ‘music servers just send bits and don’t make a difference’
The Roon forum can make anyone with an open mind look like an expert; not sure I qualify for that accolade but thanks for saying so, Surge.
In the cases where I experienced serious (frequent) "phantom playing" by Roon I traced it to local network problems -- in one case a pricey mesh router that started dropping out briefly and then more frequently until it was also causing noticeable internet connectivity problems with non-music computers, Apple TV and the like in the house; in another instance it was a cheaper unmanaged switch that started failing in a similar way.
There are network analysis tools (apps) that might help diagnose trouble spots, Fing
https://www.fing.com/ is one example. In all honesty I just easter-egged it by bypassing parts of my network and substituting known-good devices until the problems resolved. In the process I simplified the topology of my local network, which has helped immensely with both stability and ease of trouble-shooting when problems do occur, and I have the simplest possible connection from ISP-provided modem/router to Extreme:
modem/router > copper UTP jumper > inexpensive switch > 50' UTP copper ethernet > Extreme Lan 1 input.
Pretty straightforward and much less to go wrong.
Until recently I used to go directly from modem/router to Extreme via UTP copper (even simpler) , but following a tip from Emile and posts from another member here I inserted an inexpensive unmanaged switch between the modem/router and Extreme, even though the Extreme is the only device on that branch, to "insulate" the Extreme from the potentially deleterious effects of cheap modem/router combo construction and electrical performance. I had an unused linear power supply from a previous network configuration so I put it back in service with the unmanaged switch (I've been running my modem/router off another linear power supply since early early on).
Evidently, the performance of my cheap switch is better than the performance of my cheap modem/router as I heard a nice uptick in sound quality with the switch. No re-occurences of "phantom play" issues since, though to be fair I haven't used Roon in some time.
Steve Z