Recent Tracks Thumbnail is Not Showing

#1
I do have a thumbnail defined for the album in question, but in the Recent View, the thumbnail has turned into a gray question mark.

What is going on?
 
#3
They were bad for several hours, and started working right late last evening — around midnight CDT.

At first I was seeing it only on one album, but then it started on a 2nd album also.
 
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