Hi Christoph,
Unfortunately, we have no clue why this is happening. 🤔
As this issue is related with The Events Calendar, it’s best if you try to reach the plugin authors. They will be more informed and better suited to help you.
To go further, we invite you to post your request on their support forums: theeventscalendar.com/support
Don’t hesitate to share the solution with us. I’m sure it will help other users facing the same issue. By doing this, you’ll make a great contribution to this forum, and we thank you very much for that! #SharingIsCaring 💪🏻
We remain available for all support requests related with the use of your theme.
Best,