I've done some debugging and determined that the underlying cause is due to a bug in the caching layer, more specifically in version_cache_array_rows().

For the purposes of this report let's say that we have the following project_id mappings for our project hierarchy above:

Project1 = 13
Subproject1 = 4
SubSubProject1 = 20

The work of finding the accessible subprojects falls down to this line which works exactly as intended:

$t_project_ids = user_get_all_accessible_subprojects( $t_user_id, $t_project_id );

Now the problem comes when the array of the parent project/subproject are passed into version_cache_array_rows() the SQL query correctly expands an IN clause containing the project and subproject ids, but since our versions are stored in SubProject1 then all of the rows come back from the database with a project_id of 4.

As there are only rows with a project_id of 4 and no rows with project_ids of 13 and 20, the contents of $g_cache_versions_project[project_id] for these ids is set to an empty array.

Subsequently roadmap_page.php/changelog_page.php fail to find the inherited versions for the subprojects because version_get_all_rows() finds that $g_cache_versions_project[project_id] is set and returns the empty version list created by version_cache_array_rows() above. For this reason, both the Roadmap and Change Log appear empty.

TEMPORARY FIX:

Commenting out the call to version_cache_array_rows() in both roadmap_page.php and changelog_page.php fixes the bug for me, and both the Roadmap and Change Log appear correctly.