Hi Brian,
Looks like the owner must have changed 'Group-ID' away from PAWGRP, which would make the hash marks disappear as he/she was now no longer using the same group ID as yourself. My guess is that they have mistakenly put their 'aircraft ID' (Reg) in the 'Group ID' slot or just not entered their reg at all. With no entry in the Flight ID slot, PAW will transmit its 'Hex' instead - which is what you were seeing later.
Regards
Peter