Hey Franzh,
Sorry to hear about the frustrating experience.
Are you experiencing this problem while exporting a particular file or does it happen with all the files you have tried exporting?
As mentioned that you have tested with different web browser as well as computer, then it most likely trouble with the internet connection you are working on.
I believe you are working online, you may try exporting file with Adobe Reader DC desktop application- Adobe Acrobat Reader DC Install for all versions
Please go through the troubleshooting steps suggested in : Resolve connection errors with Adobe Creative Cloud and Creative Suite applications
Regards,
Akanchha