I have the same problem. I just updated to v4 from an earlier version, not entirely sure which one. This is not a site I have been actively managing lately but plan on starting it up again.
To my knowledge I do not have a child theme. Ok, so I decided to check on the browser caching by opening up the site in a different browser that I normally do not use, i.e. no cached content. In that browser the site showed up ok. So no problem except the cache. Figure I would share.
