Page Builder stops loading

After no changes to my site or its plugins, the page builder suddenly stopped loading in the static front page and all page content is open text in the page editor. Did a restore of a page revision which resulted in a similar problem and on page update, the page is broken. Restored database and got the original home page back but the page editor is calling again for an “update page” which I know will take me back to a broken page. Any advice?

Update:  Facebook Post Fixer was installed a few weeks earlier.  While it didn’t cause problems initially, eventually it was found to be the culprit.