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Have you contacted Casio or posted in a Casio piano forum?

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Without knowing your specific pianos the obvious question would be, are you using sustain pedals that are originally made for Casio or aftermarket pedals?

Are you 100 percent certain you have the pedals plugged into the correct port? You might have a Sustain pedal port and a Sostenuto port, are you plugged into the correct one? I've plugged into incorrect ports and then wondered why the piano was acting funny.

At any rate, I hope you get it sorted out and post back what how the problem was solved.

One thing you could do to narrow that problem down further is to connect your DP to a computer via USB and monitor the MIDI-Signals via MIDI-OX. Check whether the pedal signals are transmitted correctly. However - due to the error being reproduced on two different models, I suspect a software bug. Is this independent of the used piano voice?

@Dave: the Casios have only one input for pedals (the AP-620 has one input for the included three-pedal unit).

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Record it as MIDI or as a song and send it to Casio or/and put it online.
Preferrably -if possible- use the pianos inbuilt recorder.

Peter