Two pages on a very large site are exhibiting recurring problems with the core autonav block. A basic autonav black is added to an empty content area, showing 2nd and 3rd level pages beneath the parent page. Regularly, and at random, the content of this block will disappear.

The block itself still exists on the page, and in edit mode an outline will appear around the empty content block. Editing, then immediately saving again will restore the content of this block.

There are hundreds of other pages using this page type, but only two pages seem to be affected. No other issues with autonav anywhere on the site.

Deleting the block and replacing with a new autonav block causes the same issue.

Version 5.4.1.1.