WoodMart parent theme unexpectedly updated itself on two separate WP Engine site

* Both live and dev exhibited the same behavior at about the same time.
* No restore had been performed when it happened.
* No WoodMart update had been performed.
* No site push or migration had been performed.
* The site appeared to revert to orginal WoodMart state.
* WoodMart → Theme Settings → all Custom CSS was and JS was gone, just blank pages.
* The footer and header assignments were lost
* Elementor page content remained, and the CSS inside Elementor pages was still there.
* HTML Blocks still existed.
* A WP Engine restore later returned the live site to normal.
* Sucuri found no malware.
* WP Engine has no explanation.