I have an ongoing Support Ticket open for this issue. Support has been maddeningly slow to respond, hoping you guys have some ideas.
I've seen others post similar behaviour, but here it is again: Dropbox refuses to sync after MacBook Pro wakes from sleep. Pausing / Resuming syncing has no effect, and neither does quitting / restarting the app. The only thing that works is fully restarting the computer, but frankly that's an unacceptable workaround in this day and age. I'm running v186.4.6207 of the desktop app and macOS Sonoma 14.1, although the issue was present in macOS Ventura as well as Big Sur.
As noted by other users, upon opening the computer, DB will say it's Syncing... and initially display the amount of data it needs to sync. After a brief time, that data info on the right of the box will disappear and will just say Syncing... forever — until I restart the whole computer. I've seen a number of people speculate that issue is related to the macOS File Provider API, and the Big Sur switch corresponds to when I started noticing the issue.
This MacBook Pro is one of two computers I run, the other being a Mac Studio at work. I regularly bounce files back and forth, working locally on the MBP when I'm home and then logging into the Studio to render (I work in motion graphics). The issue is NOT present on the Studio, despite the machine going to sleep when not in active use. But if I close the lid of the MBP for any length of time longer than a brief instant, Dropbox stops syncing and won't resume without a restart.
Really hoping someone has figured out what this is!