Dropbox and Logic - what's happened?

Hello, I've been a Dropbox user for what feels like centuries.

For about 2 years now I've been using it to share Logic files. (.logicx) with musical collaborators who also have dropbox accounts.

For most of that time all has been well. 

Recently one collaborator uploads projects and they will not appear in my dropbox app folder.....

But if I go to that folder online, there there are in TAR/ZIPPED files?  Why?

I upload a project and they can see and open it. Why has it changed from their end?

Another user will go to our share folder, see all the files, but if they attempt to open one an error comes up stating the file is not in the right format YET, if we copy it from the dropbox folder and open it.... it opens just fine.

The very confounding thing is... that same file in the dropbox folder, that threw an error moments earlier... once it's been copied to the desktop it OPENS directly from the Dropbox folder.

What has changed?