I add a filter on the image size, individual image should be < 1MB. And I've been playing around with it. It's pretty unstable as sometime I can go through the session trouble free, but sometimes will be like this withe the exact same code.
Thanks for the update. Does the image just take long to load, and does it load eventually, or is it just not visible? Also, can you see any error message in the browser's developer console?
(I think the most likely explanation would be that the problem happens when the image is fetched and loaded from the URL as the task is rendered in the UI. So if there's some disruption there, it could result in the image not being loaded.)