Hey, full-stack dev here. I've encountered this issue as well, and while I unfortunately can't tell you how exactly to reproduce it (aside from having a bad connection/low reception), I can provide some additional details that will hopefully be of help to any dev reading this:
- The issue does not persist across browsers - though it may reoccur with a different set of pages.
- Using port 443 does not appear to fix the issue.
- Switching to low quality images only appears to solve the issue - switching back to high quality images reveals that the issue still persists for them (and vice versa).
- Rarely, the images might all reload (cache miss?) during the same session. In my case, this was likely due to leaving the page, then revisiting it after having switched networks. In this case the issue appeared to resolve itself, only to reoccur with the same pages as before upon reloading the page once again.
- The issue can also occur in Tachiyomi, though much less frequently - perhaps due to different loading strategies.
My two cents about this situation:
This appears to be either the browser/client caching and serving a failed response instead of sending a new request to the server, or a rate limiter/anti-DDoS measure that 1) blocks all requests for a specific asset if a session has requested it too many times in a row, and 2) doesn't have a cooldown system in place to allow said session to access the asset again after some time has passed.
The rate limiter/anti-DDoS option seems to me to be the more likely one (especially considering the history of this site), and is the one I'd recommend looking into first.
Feel free to ask me if you need any additional information about this problem, and I'll do my best to answer.