Upload app sync speed is very slow on macOS.

Hey all... I may be a bit late to the game here, but I too was experiencing this issue.  I was about to uninstall Dropbox and reinstall as this thread suggested, but then I realized that I had recently uploaded a ton of files (hundreds of GB's) and it occurred to me that I didn't make them 'online only' after the upload.  I checked my hard drive space and it was nearly full because so many files I had just uploaded were still local in my Dropbox folder (IE- taking up space on my computer's hard drive).  I made the folder in question 'Online Only' (you can do this by clicking on the folder in question in your local Dropbox folder once, then Control>click on the folder; from the menu, select "Make online-only".  Moments later, the space on my hard drive opened back up, I dropped 50GB's of fresh video files into my Dropbox folder and it uploaded in about 2 minutes (I have gig speed internet... Fios).  Viola!  Back to normal.  

Don't forget to make the folders within your local Dropbox folder "Online-only".  If your hard drive is almost full because you fail to do this, files will stop uploading to Dropbox.  At least locally.  

I'd imagine to work around this, to upload via web browser all the time.  That way, the files should automatically be set to 'online-only'.  

I'd put money down that the folks who re-install only to find it happening again a few days, week or months later is because they're not making the files "Online-only".