I have exactly this problem…
Please check http://alextlc.proofwebsite.co.uk/
I have completely re-created the menu from scratch and the problem is presenting in both menu’s with different header styling width settings… It does not seem to matter what I change.
I go to the settings of the menu items / Avada menu Options / Select Mega Menu & Full Width and it does not work.
Any progress on this would be gratefully received.