404 Error with Multisite and Themer

hello i have Problems

the Beaver Builder Themes makes 404
if i want open Builder Themer to makes a diffrent Page.
Header, Footer, Produkt also the same.

But thats only with BB Theme and Multisite.

After i switch the Theme to wordpresstheme and back.

this problem ends ???

Cache/permalinks, maybe both. Switching theme tends to force most hosts to clear cache for obvious reasons.