I am unsure why or how this occurs, but when using any of the sorts:
Under “Learn Roblox,”
The thumbnails will be completely blank. Switching one sort to another does not affect the blank-ness, including switching back to “Featured Content.” For some odd reason, though, this does not occur to videos or any articles with this “Golden Gate Bridge” thumbnail:
Comparing the sorts from the first image in this topic reveals:
It is very odd. A link to the “Learn Roblox” page can be found here.