Whereas VFE on the PFD is displayed according to the position of the flaps lever, the audio/ECAM warning is triggered separately by the actual position of the flaps and slats. If the slats are still in transit above 230 , the aural/ECAM warning will trigger until the system has registered that they are retracted fully.
When using the autoflap retract procedure, the buffer between a selected speed of 220kts and VFE CONF 1 (230) can sometimes not be sufficient if there is a delay after engaging managed speed before CONF 0 is selected. So, select CONF 0 & pause before pushing managed speed (250).