Fortunately this issue has disappeared, I believe it was by switching the ‚Output Device‘ setting on the second RPi running Volumio/Squeezebox to [(sysdefault) snd_rpi_hifiberri_digi]
Thanks for both of your responses. For now, two players is sufficient for my needs. I didn’t realize Spotty came preinstalled, the note at the bottom of spotify connect plugin made me think I had to set it up.
I’ve checked it out and it took me a while to figure out that the button in the mid-upper left of Settings/Advanced could be switched from ‚Formatting‘ to ‚Spotty‘. Once I did that, I was able to authorize my account and I now have synchronized streaming. Yippie.