I should have mentioned I also have an airport express in the mix. My whole house system includes several speakers running airplay one, a HomePod, 2 older Apple TVs with old airplay one software, new Apple TV running airplay 2, and old airplay express running airplay 2.
All airplay one speakers are always in perfect sync with each other. But depending on how I play music (ie from my phone, laptop, or HomePod) I get varying sync issues between the speakers. Sometimes the airplay 2 speakers are in sync with each other but not airplay one, and sometimes each airplay 2 speaker is out of sync with each other.
The airport express running airplay 2 always syncs up perfectly with all my airplay one speakers no matter what though.
So based on my experience with the above, I am confident that this is a software issue and nothing else.
It’s really really disappointing and makes it so tempting to ditch Apple.