Yes, I had, for the first time ever, a major sync failure when I moved to Sonoma (actually the beta, my responsibility of course). Here is what worked for me recommended by Dropbox email support: “Hi Sam, I also reached out to email support and I got a solution to relink my account (go into the web interface security setting and remove my laptop, then relogin etc on my desktop). This worked and cause a reindexing and resyncing that brought my desktop and web data in sync.”
See this Dropbox support thread for my problem and solution in detail, and some other suggestions if that doesn’t work…
I did end up with some duplicates including Scrivener project index files, but Scrivener is good at finding this and offering to resolve the conflict and everything worked fine after this…
As usual, apart from this, Dropbox remains far more reliable than iCloud (even though in China where I live Dropbox is blocked without a VPN where iCloud isn’t)…