Mega Menu drop down css

Hello and thank you for the wonderful theme. It is looking great on our new website except the mega menu not displaying properly at the onset of the page loading. The width of the sub menu would be the same as the parent which of course is too narrow. Usually after the full page is loaded then it’s back to normal. Please see screenshot below.

https://www.ourfamilytravelblog.com/wp-content/uploads/2019/04/menu-error.png

I had to install cache and minify plugins to speed up the site as it was very slow. I think, the menu started not displaying properly at that point and I’ve tried to turn on and off many settings to test already. The plugins I tried to change settings and turn on/off include hummingbird, autoptimize, asset clean up and fast velocity minify at one point. What did I do wrong?

Thank you so much
Anna

The page I need help with: [log in to see the link]