HIL Plane crashes at takeoff

I run HIL tests with XPlane 10 on two different machines, one running Windows but not too powerful (QGC receives XPlane at 50Hz), one much stronger under Ubuntu MATE (150Hz). Both machines run QGC 3.5.2 with recent off-the-shelf installs (not daily build).

This pixhawk 4 (with a slightly customized PX4 firmware) manages to fly its mission just fine on the windows machine, but reliably crashes at takeoff on the Ubuntu machine, e.g. https://logs.px4.io/plot_app?log=01b3deb5-280f-459c-b94b-b8067fbec501.
0:29 Motor on
0:39 starts gaining altitude (rolling left because propeller, that’s fine)
0:44 crashes, not good. Expected: should roll right and recover (what happens when it goes well).

Can you see a reason why ?

On the Ubuntu machine I have some other intermittent problems, which I will post separately.
In case they are related : sometimes the pixhawk will disconnect (COMMUNICATION LOST) ~3s after being plugged (maybe was fixed by a system update). Sometimes QGC will complain about missing parameters / unsupported firmware, with the list of missing parameters being “-1”. With the daily build I cannot see the menu bar / open the HIL widget.