The origin seems to be extremely slow, it took 28 seconds to load the site for me. I’m seeing your assets are being HIT and most of this load time is coming from the index.html (Which is always fetched from origin). I would recommend setting up a “Cache Everything” Page Rule.
This mp4 also takes an extremely long time to load: https://ik.imagekit.io/weddingcards/5_UI_S2AnDK.mp4
It is not being cached by any service from what I can tell so it seems the origin for that is also very slow.
A 524 is a timeout issue, since this site is taking such a long time to load I can see why you would be hitting this. Improve the caching and improve the response times at origin. That should solve your issues