I just did the update to Wordpress 5.01 and X theme. After the update my site appears to not request many resources e.g., fonts and images. It’s not that they’re failing to load; looking at the developer console from a client shows no attempt to fetch those resources at all.
Looking at the server error logs it appears that revslider was generating PHP warnings, but disabling that plugin makes for a clean server-side error log.
Clearing CSS caches in the Wordpress configuration and using a fresh client had no impact. None of us is a frontend developer, so we’re at something of a loss to attempt to push forward debugging.