The occurrence rate for that event is very low.
+ needs to be 30 deg or above
+ pilots need to be aware of the slats-out(plus flaps) procedure AND not be told to ignore it where it does not apply
+ the crew need to be leaving the plane AND decide not to retract the flaps OR decide to retract them during cockpit-exit sequence only after ADIRS = OFF (more likely).
Still, the awareness on these forums is quite high. Search hits for "RTLU".
A 320 After Landing Action-Query
adirs alignment and flaps 1
ADIRS Alignment and Flaps 1
Airbus FLAPS 1 after landing
Airbus Protection against rudder deflection under Normal Law...
Flaps during transit A320
Flaps on stand?