Hi Christoph,
We know it doesn’t feel good when things don’t work, but we’re here to help you if we can 🙂
The problem you’ve described isn’t a common one and so it does suggest there may be a conflict of some kind at work.
theeventscalendar.com/knowledgebase/testing-for-conflicts
I realize you marked having deactivated other plugins when you first opened this topic, but if possible it would be ideal to go a step further:
- Deactivate all plugins except The Events Calendar and Events Calendar PRO
- Switch to a default theme (such as Twenty Seventeen)
- Now visit Settings → Permalinks and ensure it is set to the post name pattern
- Test to see if you can access the main events page
If you cannot do this on your existing site, you may wish to create a test site in a subdirectory such as example.com/test-wp where you can start with no other plugins and just a default theme and begin by adding The Events Calendar and Events Calendar PRO.
Let me know if you are able to test using either approach and what the outcome is — thanks!