It appears all uploads for a pair of sites are missing from the filesystem.
This most prominently affects https://make.wordpress.org/training/. All links to uploaded images/files for the site are broken, evidenced on its front-end (namely its handbook, e.g. https://make.wordpress.org/training/handbook/user-lessons/content-editor-overview/), and via the admin media library.
Scanning /uploads (which is a mount to lan.db1.lax.wordpress.org:/home/uploads) from my sandbox confirms that /uploads/28/files/ is indeed empty.
The only other site this also appears to be the case for is https://br.wordpress.org/ (/uploads/62/files/).
Can these files be restored? Any idea what might have happened?