Hello,
I want to report issue (I believe it is bug) related to trouble with communication between your web site (https://www.dropbox.com/home) and the official Dropbox application (v240.4.8493) that normally happens on loopback port 17600:

This used to work well, but for whatever reason it shows errors on try to open some file using ellipses > Open in > Desktop. Pretty often the web site cannot even detect that there is working desktop application. At the same time Dropbox desktop application seems well working - no delay in sync, etc.
I made a little research what might be the reason and found out that despite desktop application does most of its work well there is significant delay (softly said) in responses to requests that website sends:

Such responses have to be in borders of milliseconds (1 second is a huge delay). Above delay leads to processing timeout and error seen on first screenshot.
One more additional detail: it seems that even when particular file is opened successfully at the end, Dropbox application delays it response related to the file till file gets closed. Is this normal?! It's rather BUG!
Please, forward above to team responsible for Dropbox application development.