A300...
I'm not flying the A310/A300 for some time now (I'm on A340/A330) but it just might happened that:
Once LAND mode has been armed and one AP engaged in CMD, the DC bus tie contactor (connecting the DC NORM BUS and the DC ESS BUS) automatically opens in order to assure an independent electrical power supplies for the AP/FD 1 and AP/FD 2.
In case of DC bus tie contactor failure to open, the landing capability does not change from CAT 2 to CAT 3 after the engagement of the second AP (but no audio alert is provided).
As you know FD1 receives info from FCC1 and ADR1 and FD2 from FCC2 and ADR2. In case of a slight difference of info one FD goes for the GS* and the other just acquired ALT*.
Anyway that was just a little bit strange...
Just may be one of your pax was phoning to his girl friend and the cellular interfered...