countdown to power off missing

[Wicked Stick]

I suspect that you are shutting off the power to the EFIS when the prop is still turing?

If the EFIS detects airspeed or prop RPM when power is turned off it does not start the shut down because it thinks you are still flying. It should shut down after 5 minutes once the prop stops turning.

I've also noticed during the last flight that the X-wind/wind direction readings were displaying an incorrect direction and kt readings. ???

Check your magnetometer headings for errors on a compass rose, it might need to be recalibrated.

The prop has long since stopped before I shut the master switch off to power down.

I will check the compass to see if it is off. Any reason the magnetometer would lose it's calibration over time ???
It's been working fine up until the last couple of flights.