I imagine the context is something like "the associated permissions were set by a different group or department within Google and/or decided by software running

I imagine the context is something like "the associated permissions were set by a different group or department within Google and/or decided by software running elsewhere that didn't communicate its reasoning as part of the protocol it speaks to the load balancer". That is, that's all the system generating the error message knows. But yeah, it also feels like "we (Google) don't care that much about your problem here, because nobody is going to improve this software to give you a more meaningful explanation".