I feel guilty to point at deficiencies but on top of an image not being rendered properly (which is not the platforms flaw, but your code's), image caption is missing. According to 6.5. Captions (https://instantview.telegram.org/checklist#6-5-captions) "Any captions present in the source article must be preserved. This includes captions for the cover image and captions for all individual elements of slideshows."
Yes, captions must be preserved, including for cover photos.
Type of issue
IV page is missing essential content
Reported
Jun 1, 2017
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According to 6.5. Captions (https://instantview.telegram.org/checklist#6-5-captions)
"Any captions present in the source article must be preserved. This includes captions for the cover image and captions for all individual elements of slideshows."