There's a lot of rejected events in Event-Platform service logs recently: https://phabricator.wikimedia.org/P4611
The events are related to page_properties_change schema and it's not clear where are they coming from and what have changed. The schema certainly didn't, the extension shouldn't have.

It's not critical since this event is used only for page_images->mobile_sections transclusion update, but it's better to resolve sooner rather then later.