Cannot open scrivener documents created with Mac


I have a big problem… I usually work on my Macbook but sometimes I like to change workplaces and go to my Windows PC running Windows 10.
I have Scrivener on both machines and the Scrivener folder is on Dropbox, so I can work on the same document on both.

This worked fine the last time I used it this way (back in August) but since today I cannot open or even see the scrivx files I create with my macbook, not even in Windows Explorer.
When I send the files per Email oder Download them manually they look like zip folders and Scrivener for Windows doesn’t recognize them as Scrivener files, it can’t open them.

Anyone has a guess why this is happening?

The back ups on Windows save as zip files, so the file that looks like a zip folder probably is. In that case, you need to extract the files from the zip folder (usually an option if you right click on the icon) before the project can be opened.

Thank you for your fast answer.
It still doesn’t work, even if I extract them…
And the problem persists that in Windows those files I create on Mac aren’t even visible although The Browser version of Dropbox shows em and they are in the Dropbox folder of my Mac.