See the topic below for context. @Simon_Cossar found that it is caused by a span tag with the filename. The link was created with markdown.
@zogstrip I found this bug report very confusing … but then I looked picture in firefox
We should get it fixed.
The issue is that the linked image is a WebP file which is currently only supported in Chrome.
Here’s the link to the related bugzilla issue: 856375 - Implement WebP image support - take 2.
Why some images aren't automatically downloaded?