The Dropbox desktop can only sync files when your computer is online. So, the first thing you need to do is checking your computer’s Internet connection to see if it works normally. Reconnect it if needed.
If Dropbox stuck on your computer, it is possible that your files have synced correctly but Dropbox fails to read them correctly. In this case, restarting Dropbox by quitting the program completely and starting it again can fix this error easily. After closing Dropbox, it’s better to restart your computer, then reopen Dropbox.
Dropbox syncing works when you’re signed into the same Dropbox account across the website. If you logged into a different account, then it makes sense that your Dropbox won’t sync. So, check it.
Selective sync is a feature that allows you to select which files sync from dropbox.com to the Dropbox folder on your computer. If your files are synced on all but one computer, Selective Sync may be ignoring certain folders. So, to see if the files missing from your computer were selectively synced, you can check it by going to Dropbox’s preferences > Account > Change Settings > Selective Sync.
File’s name has an incompatible character will cause Dropbox not sync issue without exception. Such as with“/” (forward slash), “\” (backslash), “<” (less than), “>” (greater than), and “:” (colon) etc. You can also use the Dropbox bad file name tool to check it.