Same here. Was looking at my “last viewed” & saw one was grayed out. Then I went to that collection & even though that one was showing, there were others that were a white blank & when I clicked on the product then the main image was also blank.
FYI, I just checked the problem product, as well as that collection – all are showing up & everything might be ok at this point. But I really haven’t done a once-over in my store to see if there’re others.
Not sure if this is universally true or not, but all the products I’m seeing with missing thumbnail images like this are photo plaques/signs with a horizontal orientation.