A number of thumbnails are missing or broken when visiting pages on Commons that have a lot of very recently uploaded files -- such as Special:NewFiles or some of the busier WLM campaign pages (https://commons.wikimedia.org/wiki/Campaign:wlm-in). Reloading usually fixes the issue.
This seems to have been been a long standing issue, but we've not escalated it before, because it's so ephemeral. However, the new campaign features are now making this a more visible problem.
The broken thumbs show up as error 500s upon inspection in the debug console; with the response below.
This issue was reported by Erik Moeller.
<html><head><title>Error generating thumbnail</title></head>
<h1>Error generating thumbnail</h1>
Error creating thumbnail:
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