Click on the Dropbox widget as shown at desktop top status bar ... get into the show recent picklist and pick a file ... it should take you to that file's new location ... did this work ?
Alternatively poke about in your https://www.dropbox.com/ to see if your files appear there
The nuclear option is to issue a find on all your files then grep its output
sudo -i # login as root to enable viewing all files
find / | grep known_filename_which_is_missing
Assure you where logged on as yourself when you issued the mv command ? and not root or another userid ?
Also issue this to view your files ... in case they begin with a dot
cd ~/Dropbox/
ls -la
and not just a ls
When you view your account from a browser is your Dropbox usage noticeably higher than normal ? is it at 100% ?
No, just myself. I checked Dropbox-nothing. Also tmp dir doesn't seem to contain anythin – Alex – 2017-09-06T20:27:08.523
could it be that there are too many files exceeding the allocated space? What happens in this case? – Alex – 2017-09-06T20:48:28.393
No it's actually just 3%...really weird – Alex – 2017-09-06T23:09:38.100