Illustration bug

Hey, since we have installed this plugin it always has problems with being right illustrated at the frontend. We just don’t know, what to do. Sometimes it works with updates of the plugin, sometimes not. We always update both wordpress and plugins. The bug is always the same, the calendar gets illustraed as a list, which makes no sense. If you wanna take a look at it, this is the URL (there is only the calendar in this page, nothing else): https://shytsee.de/shytsee-music-media/kalender/.