While indexing content some users have reported seeing that page types or other types of content appear to be initially indexed, but after the site is finished crawling exploring the index shows that no items of the expected category exist.
There has been a bug identified that can trigger this behavior within sites. An official patch has been released in EPiServer.Find 13.4.3, and a link to the public bug is included below. If the site has not been upgraded to this version it is recommended to upgrade the site. Otherwise if the site is on a later release or upgrading to this version does not resolve the behavior please contact application support for further steps to investigate.