Alt set with Guided Waypoints is not being followed

Hi. I am working on some things in SITL and sending guided waypoints for the plane to follow. I think that the plane is following the given alts at first but then it seems to accumulate alt. I am consistently sending guided waypoints with an alt of 100 meters and it gets to the point where the the plane gets up to 900-1000 meters. Not sure why this would be happening. I do send a few guided waypoints per second but that shouldn’t be a problem, right? Could there be some parameter I can set to fix this?