I also just tried on my iPhone 13 with Safari and manga loads just fine. I can tap to progress faster than the images load, but they load very quickly in under a second; if you're reading each page normally that shouldn't ever be cause for concern. I'm just not seeing any obvious issue.
We'll be looking into this further, but we tested long ago when this web reader was new and we also test on our devices whenever issues are reported, and we never run into any issues like this. You can always try these things:
Download and use the JNC app instead.
Download a different browser (Chrome, for example).
Use incognito/private browsing.
We don't know what each individual user has on their phone, with regards to apps installed, space and memory available, and browser extensions, so these are just some possible ways of either avoiding the issue so that you can read, or of eliminating variables to determine if your device or specific browser may be the problem.