Picoscope 4224 accuracy at high frequency

I am using a Picoscope 4224 and need accurate voltage measurements at around 400kHz.

By comparison to other reference equipment, it appears that the frequency response is not flat with errors of around +3% between 200-400kHz. With a high quality arbitrary waveform generator, there is a noticeable overshoot with a 400kHz squarewave applied direct to the input (i.e. very short cable from FG to PICO). This effect again is not noticeable with other reference oscilloscopes.

Tests at 10kHz are OK (<0.5% error).

I am wondering if the observed +3% @ 200-400kHz is inherent in the 4224 design, or just my particular model. It is nearly 12 months old and could have been affected by normal use. I am also aware that "20MHz" is really the 3dB point, but 200kHz is 1/10 of the bandwidth where there should be no effect, yet there are an error of +3%.

If the +3% is inherent, is there any information on the frequency response up to 5MHz?

Hi can you send an email to support@picotech.com with the image of the waveform?

Kind regards