I’m having this issue. I made no changes to the server:
Is this familiar to anyone where it just stops working out of the blue?
When I inspect the missing image, I see this:
Edit: I restored forum backups from as far as a week ago. No luck.
The images worked up to this morning. Do they depend on some external service besides Wordpress?
What can I check from Wordpress’ end?
Edit 2: Restoring a WP backup from last night did the trick. So reverting then will diff all files.
Now I’m stumped. So I restored the backup that I made before reverting to yesterday’s WP backup (the one with images not working), and now the images are STILL working.
So sure what the issue was or if I will ever find the cause.
Edit: So the issue was actually still there. (Once I cleared the browser cache) I restored backups for WordPress and Discourse as old as a month ago and still have the issue. Really strange.
Edit: I notice that Discouse has excluded importing images to to the forums. Is this because it’s problematic?
For example:
2 Images…
Images removed…
How can this be achieved because this does not seem to be an issue with config or server because I restored both WP and Discourse to backups longggg before this issue and images are still missing.
Noted. I was able to solve it. At least, I think so. I will wait a bit to confirm, then follow up next week n’ mark that thread solved if images don’t go missing again. 
I’ve slipped over these posts to here to keep the conversation grouped together. 
The solution to this - I’ve since confirmed by recreating the issue and fixing again - was:
Disabling the WP-Rocket LazyLoad feature.
I’m not sure how this conflicts (not my area of expertise), which is why I was hesitant about posting as the solution, but after testing this repeatedly, I can confirm blog images will fail to load on my setup when WP-Rocket’s LazyLoad feature is enabled.
I tried FlyingPress previously and had the same issue (worse actually, because ALL images forums+blog stopped loading) so I switched to WP-Rocket.
Now WP-Rocket works with Lazyload disabled. (Lazy loading is built-in by default a lot now anyways)
Current settings which don’t affect wp-discourse images in the forums:
Leaving this here in case anyone else comes across this issue.