I've messaged Rigel again, going to keep posting here as we try and uncover this.
Right now, we've got a time but none of the logs he sent were that helpful unfortunately. It is true that Steam is creating a error when it can't create a firewall exception, but experience tells me that shouldn't be a problem.
I've asked Rigel to research the Application Logs and either look for a typical Windows BSOD enum (like DRIVER_IRQL_LESS_EQUAL or CRITICAL_PROCESS_DIED), or a Hexidecimal number (0xC000000D) within a minute of the BSOD. If we can't find that, I'll try and grab the minidump file off him and look into that.
