Aug 6 2019
FWIW, in my previous comment I was hoping for a systematic fix (rather than having wikimedia editors have to fix images one-by-one). Do we know why some images are served with this weird application/x-www-form-urlencoded content type? I would normally associate application/x-www-form-urlencoded with http POST *requests* rather than with http *responses*...
This bug caused some images to be blocked by Cross-Origin Read Blocking (CORB) in Chrome 76 - see https://bugs.chromium.org/p/chromium/issues/detail?id=990853#c2