@timm1996 I found a solution for my problem. As I stated, I couldn’t see anything in the general or the debug tab of the plugin (and couldn’t use the form tags, nor customization of the send button). If you have the same symptoms this might help.
I managed to solve it this way:
1. Go to Divi -> CF7 Styler, the page is empty
2. Go to the debug tab (the page is empty too)
3. Do a browser refresh of the page and the debug info should be visible.
4. Go to the general tab and everything should be visible there too.
The problem is solved now and everything works again.
Good luck!
Jurgen