Relative altitude discrepancy in AUTO mode

Hi all, new here but wanted to ask a question about some issues I’m having with ArduPlane and planned missions.

I’m working with a small flying wing designed to be deployed mid-air and land at a target location. We’re currently attempting to optimize the autonomous landing process for this airframe but are having trouble getting the aircraft to obey simple missions.

The aircraft flies as expected in manual and FBWA, but as soon as the aircraft is switched into AUTO mode, the aircraft attempts a rapid climb, even when its reported altitude less the aircraft’s home altitude is greater than the relative altitude desired at the first waypoint. We’ve seen this a few times, and have been trying to diagnose it, but are kind of at our wits end.

We wanted to ask if anyone had experienced anything like this before, or might have any clues as to why it might be happening. We’ve boiled it down to there being some discrepancy between the actual relative altitude and what the vehicle believes to be the relative altitude, but in digging through logs we’ve been unable to pinpoint the cause.

The vehicle is equipped with a rangefinder, so is there any chance that the vehicle is taking the rangefinder’s reading as truth, I believe it maxes out at 11m or so, and in the log file I’ve attached, the first waypoint is set at 20m.

Apologies if this isn’t the format/place to ask these sorts of questions, let me know if we should be looking somewhere else. We greatly appreciate any assistance!

Here’s the .bin file, if helpful.