On some communities the header image and community logo is broken, e.g. here: https://lemm.ee/c/idm
I’m the mod there, I haven’t changed images since I started the community, a year ago. If I click on the Edit community button, I can see both images on the sidebar.
If I comment somewhere and link to external image with the markdown syntax  images not showing up. This works in post bodies, it only affects comments.
Created a test post here, you can see the image in the first comment is not visible: https://lemm.ee/post/38021843
Edit: This may be related: https://lemm.ee/post/37717282
This image appeared Ok for me
But on the test post in the test community you can’t see this comment, with an image: https://lemm.ee/comment/13560597
Yes - when I follow that link, it takes me to the “view comment thread” view which should show me that specific comment and replies. However it does not show any comments for me