The Select Media dialog box might show different results in the List view and in the Tree view. Newly created unversioned media items are missing from the List view if they use the shared Media field, due to an incorrectly applied language filter.
To resolve this issue, for Sitecore XP 9.0.2 and earlier, download and install the patch compatible with the affected product version found on this page: https://github.com/SitecoreSupport/Sitecore.Support.95446/releases.