the fixedwing code is split in FBW and AP
I think you now have AHRS_TRIGGERED_MAIN_LOOP set in your airframe file, which waits for AHRS(Xsens) messages to then compute control commands with absolutely minimal delay (just when they were received) and does only compute new control commands when new attitude data is available.
If for some time the FBW does not receive any control signal (e.g. on XSens startup or without any XSens connected) then it informs the user that the AP is failing: (not the FBW) and suggests to switch to manual mode, and if you don t it activates the failsafe mode (until either manual mode is selected with the RC or the AP starts giving data)
If you remove the AHRS_TRIGGERED_MAIN_LOOP, then you will not get this message anymore, but if you do not receive data from the XSens, you will not get any warning either, which in my opinion is less safe.