I've had both 622s and 722s do it, but it was software-related. My present 722k used to do it but not since it downloaded the latest version.
Even if it wasn't caused by the present software, your receiver is still in effect a computer; so yes, it's normal for a locked-up computer to re-boot itself. Sometimes you may even have to help it a bit and force the re-boot, but that's the way it goes.
By the same token, a bad receiver or a faulty installation will cause the same, but that is usually an issue that is permanent and doesn't clear up by itself. That should be an indication to you that you need to chat with a CSR or a DIRT member.