Macs playing multicast stream used to stay in sync, now don't

[degoffo]

I've been using VLC successfully for a few years to play a multicast video stream (from a different streaming server) on multiple Macs in sync with each other. It just worked, both over Ethernet and over wi-fi using a multicast-to-unicast feature of my WLAN. Now, for the past few weeks/months, the Macs are all out of sync with each other, by up to a few hundred milliseconds. The Macs had ended up not all on the same version of VLC, so I got them all on 3.0.18, but that didn't help. I've played with different VLC settings--network caching and other things--making sure all the Macs have the same settings, also with no luck. Any ideas? I'd like to try reverting to an earlier release to see if this is an issue with the VLC app that crept in at some point...any suggestion for the best earlier release to try reverting to?