on an API v2 packet between two xbee S2B's, get a discovery status of 0x43

once in a while, when I send a packet to a pin sleeping end device from a route, I get a discovery status back with the hex 0x43. This is not in the manual. What does this status type mean?

I believe that is now listed in the Frames interrupter in the XCTU 6.x.