It the plugin “Jetgridbuilder” by Crocoblock that caused the issue.
I deactivated that plugin and now site creation works fine.
No, not exactly like vertical-mega-menu (if I havent missed something in the documentation).
You can have a look at https://shop.fronta.se/ to see how I want it to behave.
At the bottom of the header you have “Inspiration”. If you hover it a menu expands to the right on the same row, those 3 are actually sub-menu items
[Top item] [sub-item 1] [sub-item 2] [sub-item 3]
Found the solution.
In plugin settings, the section “Advances settings” there is a checkbox “Allow blob”.
