We noticed that the cache was not being cleared after one of the articles was vandalized on wikidata. This is the history of the article in question: https://www.wikidata.org/w/index.php?title=Q16148924&action=history.

Article was vandalized on June 16th and the change was rolled back the same day. We got our first report of the issue on June 18th. The response was still returning an incorrect thumbnail url on June 21st.
Editing the Wikipedia article (https://en.wikipedia.org/wiki/Farrah_Abraham) fixed it.