HELP pls - when someone adds a variant they find another in their cart + search and main menu doe

[mylittleworld]

Hello

I'mm having issues on my website www.mylittleworld.shop

there's suddenly a grey background pro the logo in header. also the search shop and marketplace buttons in header are unclickable. 

But the bigger issue is that when someone adds something into their cart, at check out it's a totally different variant that's added. 

Please help!