I had the same issue after upgrading to 4.0. I turned off ALL plugins, upgraded enfold, same issue continued.
I then RE-updated 4.0 wordpress and closed browser (cleared cache) and opened again, it works for me, however, a customer who I made the site for still sees the spinning wheel of death. I have asked them to clear their cache and try again. will update.
For those who are following the directions to clear, dont forget to clear cache (and close ALL browsers, if your like me several open at once they retain the cache until closed) then try again. works now for me (just not customer whom it is most important for.
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I can confirm 100% that it occurred for me today after updating WordPress and wasnt cleared until after Enfold was updated and WordPress Re-Installed.
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UPDATE: Customer cleared browser cache and is now working again for her.