Hello Gӧtz,
thank you very much for reporting back.
I am glad to hear that you managed to solve the problem. However, this seems like a bug on our side. Using Save as function should create a new project file and folder independent on the previous one.
Which drive did you use for saving the project and cache? Was there enough space available? In order to fix this issue, we need to be able reproduce it. Therefore, any additional information would be very helpful. Thank you.