Thanks for coming to the Community, boberonicus.
I appreciate the information you've shared and the effort you've done just to resolve this issue. I want this to be taken care of.
Since the necessary troubleshooting steps you've tried didn't work, I'd recommend you get in touch with our Customer Care Team so they can open an investigation. This way, they'll be able to know what's causing this unexpected behavior and use a special tool to take a closer look and provide a resolution.
Please know that I'm just a reply away if you have any other concerns with QuickBooks Desktop. I'll be around to help you out.