$ curl -I https://upload.wikimedia.org/wikipedia/commons/thumb/8/8f/Isoetes_setaceum_Habitus_2010-10-03_FuentedeSanLorenzoSierraMadrona.jpg/250px-Isoetes_setaceum_Habitus_2010-10-03_FuentedeSanLorenzoSierraMadrona.jpg HTTP/2 404 date: Mon, 17 Jun 2019 12:01:18 GMT content-type: text/html; charset=utf-8 content-length: 1836 server: Varnish x-varnish: 158709953 x-cache: cp3038 int x-cache-status: int-front
But the Image exists on commons:
$ curl -I https://upload.wikimedia.org/wikipedia/commons/1/1a/Poaceae_Habitus_2010-10-03_FuentedeSanLorenzoSierraMadrona.jpg HTTP/2 200 date: Mon, 17 Jun 2019 12:02:02 GMT content-type: image/jpeg content-length: 3663033 x-object-meta-sha1base36: 9gclsax9nls33aj9l94mcbk6r7ox6wv accept-ranges: bytes last-modified: Fri, 14 Jun 2019 14:31:38 GMT etag: 7a0f64eaaebd0258ea8a0beb72e255f6
So we have here a kind of rendering/scalling issue in the backend. In that case, the HTTP error code should not be HTTP 404 IMO, it should be HTTP 50X.
It looks like a detail, but the problem is that currently there is no way to make the difference between a missing image and a thumbnail rendering problem.