Huge gap in tab section

“Hi there
please have a look here:

In the Tab-Section there is in…
-https://skepkon.gwup.org/vorlage/#donnerstag
-https://skepkon.gwup.org/vorlage/#freitag
-https://skepkon.gwup.org/vorlage/#samstag
…a HUGE GAP between the tab section and the content

In https://skepkon.gwup.org/vorlage/#referenten not.

Please let me know how to fix the “huge gap” issue
“Its not due to our custom CSS.
We checked that”
thanks
andré”