I think I might have experienced this too. I did some reload clicks, and some shift-reload clicks, and they didn't help. Then I did a 'new circuit for this site' click and the problem went away. That is alas my only hint for now; I'll add more details if I hit it again.
https://www.shroomery.org/forums/ also does not show avatars, post icons, smileys and favicon. Picture thumbnails display/load fine but clicking to magnify/zoom fails.
I do not think it specifically CF hosting related, some other forums I frequent are definitely cloudflared and do work fine. Not sure if it's helpful, but apparently shroomery.org/forums/ uses files.shroomery.org for serving images (some, not all) and I get 403s when looking at the problem images in inspector>network>images
Attempted Safest, Safer and Standard security levels, used New Identity as well "(i) New Circuit" numerous times, no changes. also tried all manner of permissions given NoScript and HTTPS-E on/off and EASE on/off.
Seems to be caused by "Accept" header, which now is "image/webp,*/*" instead of "*/*" in the previous versions (this changed in Firefox with introducting the webp images support). Some servers somehow don't like that and return 403 error instead of a image.
\o/ Make it a child of the CF issues metabug, so that everybody can see what harm CF can bring to them, and that it's not tbb-9.0-issues.
The Tor project is not siding with Tor users. They refuse to cooperate a long time ago.
It's a shame the Tor project is NOT fighting against global surveilance!