HI Thomas,

"Kontakt" menu item shouldn't be separator (!) this menu type is not for typical menu items, it's like comma!! Joomla developers kept since J1.x as part of legacy, but please do not use it.

Change menu item to normal link. Then it will be OK.

OR as alternative use that

.offcanvas-menu .offcanvas-inner .sp-module ul.menu > li > span {
  font-size: 22px;
  font-weight: 700;
  text-transform: uppercase;
}