AP_OpticalFlow: only publish PX4FLOW data few frame to MP then stopped

[bys1123]

Issue details

MP can only show the first frame from optical flow. But the log shows it works well.

Version

Copter-3.6.7~3.6.9

Platform

[ ] All
[ ] AntennaTracker
[√] Copter
[ ] Plane
[ ] Rover
[ ] Sub

Hardware type

Pix32(Pixhawk), Pixhawk4

Logs

tlog:
https://www.dropbox.com/s/8mos4rk87wtbm38/2019-05-04%2021-15-39.tlog?dl=0
ArduPilot/MissionPlanner#2141 (comment)

other person have the same issue:
https://discuss.ardupilot.org/t/how-to-setup-and-check-optical-flow/20444/40

[bys1123]

Tried CX-OF today, values of opt_* still not updating.

[bys1123]

The reason why it's not have optical flow status data reading because of I didn't connect rangefinder, I got output after I connect a VL53L1X lidar, Is this expected? @rmackay9

[rmackay9]

I think we've resolved this in Copter-4.0.0-rc1 (#13182) so I'm going to close this if that's OK. Happy to re-open if we find the issue persists.