Mavlink msgs with HUD information are not sent for a few minutes after takeoff

Hello to all,
I have found a weird problem with firmware ArduPlane 3.9.4 on a BORMATEC Maja plane. Some of the information of the HUD in mission planer (specifically, airspeed and ground speed) stop updating a few seconds after takeoff. It has happened in all flights with 3.9.4 firmware.
After exporting the telemetry logs to text to see the mavlink packet, I have noticed that the MAVLINK_VFR_HUD message that contains the air and ground speed is not sent by ArduPlane for a few minutes. For example, after this message:

26/01/2019 13:18:06 FE 14  0  0 D3  1  1     4A mavlink_vfr_hud_t airspeed 14,55071 groundspeed 12,31533 alt 36,28 climb 3,776273 heading 233 throttle 86  sig  Len 28

the next one is two minutes later:

26/01/2019 13:20:15 FE 14 0 0 19 1 1 4A mavlink_vfr_hud_t airspeed 1,274226 groundspeed 0,996267 alt 18,82 climb 0,4071487 heading 295 throttle 0 sig Len 28

We are using an airspeed sensor and I have read a discussion in GitHub/Ardupilot about not sending the airspeed data if the airspeed sensor fails, but I don’t think it is always failing just after takeoff, and there are other information in the mavlink message that should be sent anyway.
I will apreciate any suggestion about this issue.

Thankyou very much in advance for your help,

text versión:

Do you have an on-board log from the autopilot? That would give us a bigger picture as to what is going on on the other end of the link.

Thankyou Nathan for your help, the dataflash log is here:

However, this dataflash log includes several consecutive flights and there is a shift in the hours of each one, so I am not sure at the moment the matching timestamp of each one. I think that the onboard log includes correct values of ground and air speed.
The only weird thing I can see in the dataflash log is that the altitude measured by the rangefinder (terarranger evo 64) is , at most, 5 meters, which is weird because the value of RNGFND_MAX_CM is 5000cm, that is , 50 meters, however, it seems to work only up to 5 meters. Yet more weird, the missing mavlink packets are in the middle of each flight, which correspond more or less with the time span where the rangefinder is not working. When the airplane is taking off, and when it is landing, at low altitudes, the mavlink messages with air speed, ground speed, climb rate, etc. are sent ok. just a coincidence?

Any help will be much appreciated,