Are you using groups with snapcast? Lat time I used it that was a major pain in the ass and made me switch to squeezebox.
Afair the groups were named on the fly and you couldn't create static ones (downstairs, house for example)
EDIT: Found one of the threads and it is still open. https://github.com/badaix/snapcast/issues/308 Seems there is a workaround for home assistant, but that doesn't look like it is really stable so to speak. I guess I'll stick with squeezebox for now, the sync feature is good enough for me.