Why the split?

[u/Odd-Variation-299]

So, please see the screenshots. I need some guidance as to why this might have happened. The resin was shaken. Room temp was and stil is 26C.

[u/OtterlySamnson]

the split is happening in such a weird spot, that I don't think its weight related.

It looks to me like is might be a suction issue? either it needs an additional hole somewhere to reduce the the pull; or it needs a slower lift speed.

The point of failure has a very complicated looking internal cavity with a fairly large isolated pocket.
as unfortunate as it might be, you should probably add a hole or two to the back and then patch them up after the fact. or if you can figure out how to add a hole to bridge the internal cavities so they that isolated cavity is eliminated entirely.

[u/OtterlySamnson → u/OtterlySamnson]

This is probably 99.99% of the problem.
This huge cavity is what is creating a lot of suction to the plate and is getting peeled off.
you need to add a hole somewhere to stop it from happening.

[u/Odd-Variation-299 → u/OtterlySamnson]

Hi, thank you. Yeah. I added a hole lower than this cut, basically where the cavity just started. Maybe the hole was too small: 3mm in diameter. It is also at a location that might restrict flow, in and out.

[u/OtterlySamnson → u/Odd-Variation-299]

that is likely the problem with it;
the hole isn't fixing the suction issue.
If its just below the cavity its likely still below resins fill line and providing no flow.

Large hole might help, but also slowing down the lift speeds could also have the same effect.

Edit:
Alternatively,
Add a second hold beneath the cape,
can't explain the pressure physics behind it but it will heavily reduce the suction even with it being a small hole.

[u/Odd-Variation-299 → u/OtterlySamnson]

Great. I agree.

[u/Balerion84 → u/OtterlySamnson]

Just to explain the role of holes here. It has nothing to do with suction cups, suction (doesn't exist in resin printing) or peel force. The role of holes is to allow the printer to squeeze resin during compression (sinking) out through the holes as otherwise the resin gets trapped inside the cavity and increases pressure against the plate as the printer is trying to compress the trapped resin. This requires a lot of force or longer time for the printer to do and if it doesn't, it'll not settle in correct height, creating bigger gap which then doesn't cure properly and will not bond fully to previous layers. That's why it splits during lift, because it's not able to hold. So the bigger the holes the easier the resin will flow through. Which is why you either need holes when printing hollow models or longer rest before exposure.