I'm a bit late to this, but you could have saved quite a bit of time trying to unlock that chest if you just turn on the option to let you retry failed 'exploration checks.' For some sake of preserving the original rules I think there should have been an intermediate option where you can only retry after a long rest or level up. But it does seem stupid that in the core rules, a character can never try again, no matter how much they improved since that original attempt.