When a user tries to search a site in SharePoint Online, some results or pages may be missing from the search results. For example, the following may be missing:
This issue may occur even though the site was crawled and indexed by the Search service and even though the user has permissions to access the resource by using a search query.
To resolve this issue, check the site's search visibility options at the following location:
Make sure that the Allow this web to appear in search results option is selected.
Parent site and sub site-specific search issues
The default setting for search visibility is one of the following:
Do not index ASPX pages if this site contains fine-grained permissions.
This site contains fine-grained permissions. Specify the site's ASPX page indexing behavior.
If a subsite on the site collection doesn't inherit permissions, .aspx pages won't appear in the search results. To resolve this issue, set the search visibility option in Srchvis.aspx to Always index all ASPX pages on this site or Always index all Web Parts on this site, depending on which option is available. Additionally, you may set the subsite to inherit permissions from the parent site.
For more information about search, go to the following Microsoft websites: