[Geschlossen] 404 page

Background of the issue:
I am trying to resolve a 404 page error that occurs only when the WPML plugin is active. The issue can be seen on this page: versteckter Link

Symptoms:
We are getting a 404 page error when the WPML plugin is active.

Questions:
Why does the 404 error occur only when WPML is active?
How can I fix the 404 error related to WPML?