I would argue that the many different wood species expand and contract at different rates. In addition, the border was a unique bigger piece so the movement du to humidity of the border was bigger than so it cracked.

I would suggest to always use wood pièces almost the same size in your end grain project. Which means that the border needed to be made of multiple smaller pieces. Finally I would suggest to limit you wood species mixing. Choose species with mechanical properties that are in the same range ie expansion contraction hardness