I’d like to update: after fiddling with some setups, it suddenly started working when I un-checked the HIDE ARROW (so the arrows came back to the menu), saved, and then checked it again.
This was from APPERANCE-MENUS-MENU STRUCTURE and then selecting the menu item, clicking the blue button with a nut inside.
Weird… but solved. I wanted to comment just in case it was of help to any other person.
Thanks for posting your findings. Unfortunately the same didn’t work for me.
I just wanted to say that the same error happened again, after updating Nirvana Theme to a newer version.
Even if I am using a Child Theme based on Nirvana, after updating, I had to modify the header.php of the Parent Theme as described here:
https://www.maxmegamenu.com/documentation/nirvana/