when clicking on drop down menu item, the submenu is expanded properly, but off canvas menu closes.
we could only reproduce it on firefox so far https://recordit.co/mmWCNBDFaU
It seems that the dropdown menu item points to an actual page, but it’s not possible to go to that page since you’re using the entire menu item as a click dropdown.
What I would do is replace that menu item with a Custom Link menu item with # as the URL – that should fix the issue.