Since several months I am finding that Dropbox sync's very slowly, but only for uploads. All suggested solutions do not work. I have set the bandwidth to the maximum.
As a work-around, I log into the Dropbox website and upload the file manually. This upload only takes a few seconds (so the speed of my connection is not the problem), but I then get a mail "we noticed a new sign in to your Dropbox". Uploading the same file through the regular syncing process can easily take 30 mins to an hour.
Any suggestions what is causing this? I did not used to have this problem, and using sync to download files also goes very fast.