AWS is so secure that even with full access I cannot access the resource I need and the error message is so cryptic every hacker will give up first. Amazing!

Security by obscurity right there! :)

if an execution on AWS Step functions is too old on our systems it just doesn't show up and keeps looping

AWS permission model is deny last.

So even if you have full access, say, by being in the administrator group or similar, if the specific resource policy (or any other role policy) denies your role from accessing it, you won't be able to access it.

Of course, if you do have admin access, it's simple to remove any such policy.