Scrivener does not save in USB in certain circumstances

I try to explain it. Im from Germany so there might be some weird wording. If something is unclear please ask.

I am using Windows 10 Version 1803 on a Netbook (Lenovo ideapad 120s 11IAP).

When I go to Dropbox and double click the data I want to open it opens just fine.
When I then try to save it on USB or microSD I get an error message. It says the project could not be saved because a Project with that path is already opened and has to be closed. (I put a picture of the message in, but it’s German)

If I open scrivener and Open the project over “Data” and “Open” I can save it everywhere I want.

If I open it over recent Projects I can save it everywhere I want.

If I open one from USB/SD with Double click on what I want to open it seems to work just fine too. Didn’t extensively test that though, just once for saving on USB/SD again and once for saving it on Dropbox then.

I don’t know what causes that bug with Dropbox (If it is one) but maybe you can figure it out.