what does the RP stand for here? ie: standby RP
NSR disabled on neighbor xxxx:3:2000:3::35 on standby RP due to BGP Notification sent (VRF: default)
downstream RP is not healthy
and is this different than the RP in the XR hostname I'm sure it would be something unrelated...
what does the RP stand for in the hostname area?
Is this physical or virtual? If the former, which platform is it?
RP is Routing Processor - the "brain" in IOS XR. The log messages you are seeing is likely because the active RP (RP/0) is tearing down its TCP connection to the remote peer, and thus disables the Non-Stop Routing (NSR) for that TCP session (and subsequently the BGP session, which gives you the NSR messages about the IPv6 neighbor) on the standby RP (RP/1).