Hi there!
I'm using Dropbox on two laptops (Windows 10) and they both have had this problem recently - to be exact, the problems pretty much started with the last Dropbox update.
I tried uploading some phone backups into Dropbox, but it started only saying several thousands of files were syncing while giving a way to small file size (between 200 MB and 1 GB, while the files were around 80 GB). I then decided to try and delete these files, but the problem persisted on one of the two computers. One stopped after a while, without having synced anything, but the other one says that over ~33000 files - 1 GB are being synced (~16000 indexed and 16000 downloaded). The numbers don't ever go significantly down, only up. It does not mention an estimated time, though it did before, changing between 1 second and 2 or more days. I've tried deleting the files on the other devices I use as well, clearing the Dropbox cache and the PC bin, letting a cleaner run and letting the system search for broken files repeatedly, but it just starts back up every time I start the laptop.
I would try deinstalling Dropbox but the laptop in question is using the PC Backup and I don't know whether it will reintegrate into the old backup again (if I can keep it at all, if not, I definitely can't deinstall Dropbox) or whether I'll have all my files twice afterwards/a new PC backup, which I do not want. Since I added some files while the laptop wasn't syncing correctly, I'm not sure whether it would be able to download them?