Altitude lost and regained in Guided mode, but holds steady in Auto mode


When I execute a flight plan in Auto, the quad holds altitude nicely as it moves from waypoint to waypoint.

When I change the flight mode to guided using the Tower app and command it to fly the quad steadily loses alt till it gets to the destination, then climbs straight up to the original altitude. It seems like it would totally fly into the ground if given enough space.

This is not a problem per say, I would like to understand the behavior/logic, and if possible improve it.