Hi,
I have the same problem. With you have Astra and transparent header activated and install Yith Wishlist, the header goes white.
Like this:
View post on imgur.com
When I deactivate this plugin, my site goes normal:
View post on imgur.com
I have the same problem, an hour ago I was working normally.
I uninstall all the plugins and reinstall nextgen and still not visible in the wordpress menu.
