I added a HomePod to my group zone, and I could see that the latency problem only applies to Audio Pro C10. The other Airplay speakers (Pioneer A4 and HomePod) work perfectly in sync.
What strikes me as odd is that this issue only occurs when I’m using Roon. If I use “Music” from Apple (the new Itunes), the speakers work perfectly. The same with Airfoil. Only Roon has this issue with Audio Pro C10. I don’t know why, but there is possibly something with Roon. Otherwise, the same issue would be found in those other softwares.
Any clue? The network works perfectly (and this would not be the problem, because of the perfect sync when I use those other softwares… it is the same network, after all!).
It is out of sync at the start, though I have already noticed that it can get worse over time, I guess.
I installed an airport express connecting to the Line In of Audio Pro C10 and it is now in sync. The problem seems to be with Roon and the AirPlay embedded in the speaker.
The problem with the Audio Pro embedded Airplay only happens when using Roon, not iTunes, Airfoil, etc, so I think there is an issue between Roon and this speaker.