I had a paid subscription but canceled because of their attitude on this. When dropbox.exe can't sync a file because of some file permission or other access problem, it just consumes huge amounts of CPU trying over and over. There is no notification of a problem. There is no log. There is no place in the interface where you can look to see what file is causing the problem or even that there is a problem. You have to just notice the CPU usage.

When I told the support person that this was a problem, he flat out refused to open a ticket or file a bug report. He denied that this was a problem!

That was a couple of years ago, so maybe they have improved since then, but I'll never find out.