Bridge & your devices · Collab Sync
What happens to Collab Sync while the other Mac is asleep or offline?
Short answer: Collab Sync just waits. When the other Mac is reachable again it does one catch-up pass, sending each changed file once with its final contents, and the folders are back in step.
Nothing piles up. Collab Sync waits, and the moment the other Mac is reachable again — on the same Wi-Fi or across the internet — the two folders do one catch-up pass and they're back in step.
A file you changed several times while disconnected is sent once, with its final contents. Meanwhile the folder shows Waiting for ‹the other Mac›.