Why did my Butter Mochi Split?

First time making butter Mochi and I followed this recipe- https://pintsizedbaker.com/taste-of-home-butter-mochi/

I didn’t have coconut cream so I replaced that with more milk which may have been my problem? I also did not have a glass 9x13 pan so used 6x9 pans. I assumed it would cook quicker so I checked at 30 mins (not done) and then at 45 mins. I did not wait until it was done cooling to cut into the first one but noticed that I was split.

I thought it might not be done cooking so gave it another 10 mins. Both pans ended up with this split but I did confirm with an internal thermometer that it was above 180F so the egg in the recipe should be safe to eat correct?

Can a more experienced baker or someone who cooks a lot of butter mochi tell me what went wrong?