Sorry for not answering not earlier but I was in the end on my thesis and had to focus on the dead line. After that I needed a few days off.
Now I want to come back to the sync problem because I want to work with other people on my base to enhance it to a later product - probably/hopefully.
I have the feeling that the computer on which I did the registration is in a way the leading one and unfortuately overwrites files on the other devices.
I have to solve this insecurity before I can go further an collaborate with others. Is there anybody who has some similar experience?