How to fix mime-type and (after disabling nosniff) 404 errors for css and js files in staging site

I set up a staging site from the live site with my hosting, A2 Hosting. The pages are all messed up, and in the browser console, I could see lots of mime type errors (photo for examples). The errors come from CSS and JS files from all the plugins and theme.

Mime-type mismatches in Browser console

I talked to hosting support, and they edited the .htaccess file to disable nosniff, so the browser can see what they really are. But now they are generating 404 Not Found errors in the Network tab of the browser developer tools. But if I copy one of the URLs from the error and put it in another browser tab, it comes right up, no problem.

This makes no sense to me, and I would appreciate a pointer how to fix it.