According to FCOM 1.22.30 p69 "the FMGS synchronises the A/THR, approach capability and AP/FD modes to provide identical information on both PFDs."
I think it is a flight phase related matter. In this condition both FMGS are in approach phase, as we can see in the picture both are on THR IDLE and both have the same approach capability. The (big) difference is that one system is erroneously in flare while the other one is following the ILS. As the RA1 reads an erroneous height value, it triggers the flare on the FD/AP 1 while the other FMGS, receiving inputs from its onside RA2, has no logic to trigger the FLARE because it actually wouldn't know the reason to do so. When I say it is flight phase related, I mean that there is no flight phase change at that particular moment between the two systems, so they are indeed synchronized...