Hey guys. I was having the exact same problem and literally tried everything. – including the downgrade and re-install, google libraries plugin, new wp-includes, clear cache …
none of it worked.
SO I deleted my .htaccess file and it’s now working!!!!!!!!!!!!
I am soo happy! SO delete your .htaccess and see if that fixes it!
It should be in your cpanel public_html
Make sure that the “Show hidden files (dotfiles)” is ticked.
Then delete and the problem is fixed (at least, it was for me!)