[Bug] Fixed-wing can ignore position setpoints in Offboard mode, potentially leading to an uncontrollable speedup and a crash

[mmpro881-crypto]

Describe the bug

Bug description

During FW flight mode with a standard VTOL configuration, when switching the flight mode from Position to Offboard, it can happen that the vehicle ignores the stream of position setpoints and continue flying straight. In addition, when this occurs, the flight logs indicate that the FW may begin accelerating uncontrollably, potentially resulting in a crash.

Related issue is in #12517

Reproduce

1. Start SITL Gazebo classic simulation and choose standard VTOL
2. Arm and takeoff in VTOL mode
3. Once the vehicle is in FW mode switch to Offboard
4. Fly some time in Offboard then exit Offboard and go immediately back to Land mode
5. After point 4 vehicle will automatically transtion to multicopter mode
6. Don't let Landing to finish but instead go now to Position mode - Optionally, prepare the vehicle so that an immediate transition to FW will occur after entering Position mode.
7. Transform vehicle to FW if not already and activate Offboard mode
8. When the bug is triggered, the vehicle continues moving approximately straight ahead and does not respond to valid Offboard setpoints.

Steps 4 - 7 need to be repeated since the bug won't occur always.

Vehicle Parameter Configuration
The vehicle speed was configured to 50.0 m/s for both the Multicopter and Fixed-Wing (FW) configurations. The existing 25.0 m/s speed limit was removed, and the roll and pitch proportional gains were reduced to ensure smooth and stable flight at higher speeds.

Expected behavior
When provided FW with a valid stream of position setpoints in the Offboard mode it is expected to follow.

Flight Log files

1. https://logs.px4.io/plot_app?log=729db02a-eddf-4181-a41c-6f7c7876c3a5
2. https://review.px4.io/plot_app?log=c06fb3c2-5fb1-49fb-accc-1d7b7cea0540
3. https://review.px4.io/plot_app?log=9455fde3-c183-456d-bd1c-c04c191baa9b

Above is the image of the vehicle movement taken from the first flight log file and stream of position setpoints. Circled in red is the area where vehicle is in the Offboard but ignores provided position setpoints.

Affected Software version
PX4 1.14.3
Simulator: Gazebo Classic
Vehicle: Standard VTOL

[julianoes]

FYI @sfuhrer

@mmpro881-crypto the question is now if it still reproduces with v1.18 or main, and if not, where we fixed it. Do you know?

[mmpro881-crypto]

@julianoes It can be recreated on v1.18.0 (RC) as well. Multicopter follows Offboard setpoints while Fixedwing ignores entirely and just flies straight. Flight log: https://review.px4.io/plot_app?log=4b9e70fa-160c-42fd-8efe-314784063611

[julianoes]

@Jaeyoung-Lim any ideas?