Why does the distance sensor fail suddenly while the copter is hovering?

Flight Testing & Log Analysis v1.15
1

After rebooting, the copter functions normally. This has happened on several occasions.

Any idea frome the log?

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2

Why we lost op data switching from offboard to descend?

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3

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flight assistant said it is likely a distance sensor hardware/driver failure

here is the chat

4

I also do not think this is related to the mode switch.

Distance sensors are not known to be extremely reliable, so having one fail is plausible.

5

Yes, it’s NOT mode switch issue.
It seems there are op data lost before mode switch.

Time Event
39.66s Distance sensor starts (normal operation)
40.62s Optical flow starts (low quality)
86.61s :warning: Optical flow STOPS
88.05s :red_circle: Distance sensor STOPS (root cause)
90-93s System dead-reckoning without ground reference
93.26s :police_car_light: FAILSAFE: OFFBOARD → DESCEND
93.26s+ Position control disabled, altitude-only control