The same problem.
Before the latest update i have used 'separator' or 'menu heading' menu item types for 'blank' menu items which has dropdown.
I think its all due to https://github.com/t3framework/t3/issues/237 this closed issues.
Site on localhost, so no example.
What menu item type i have to use for blank ( no link, just separator which has nested or child items) menu items?