400 Bad Request and bad loads

Hi Everybody, probably Ben;)

I am not sure if this is a problem I should address here or at my domain provider. So please tell me cause then I will call them in stead!

Anyway a problem I’ve been having is constant needing to reload every page of my website. Every view page views it shows the page horribly. As if he is not loading all the css and/or scripts. Everything looks mixed together and shift all over the place. This happens in the wordpress dashboard just the same!
What I have to do is reload the page, sometimes twice, and then it will be looking normally again. This happens a lot!

Also, not as much as the other problem, I get a 400 Bad Request page. Same here, just reload and then it will be back again.

I am using Firefox, but it also happens on chrome. I have it on all my computers/laptops and on different internet connections. I have it both on the viewing page of my website as on the wordpress dashboard behind the scenes. But I do not have it while viewing other sites. So it is my website that’s causing the problem.
I am using a child theme, especially the header is really different because of the extended menu. And I use plugins (also woocommerce) but not something different or new.

I would love to hear from anyone! My website is: Brigitte Dam Jewelry Design