Loiter_to_alt and guide mode doesn't work if I set Q_guided_mode to 1

Hi friends:
As I describe, the Loiter_to_alt and guide mode doesn’t work if I set Q_guided_mode to 1. And when I set Q_guided_mode to 0, it works well.
And another problem,when i set Q-RTL-MODE to 1, in the "Land descend started"stage ,the descending was twitching,down_spd was ranging from -3.5m/s to 0.2m/s ,actually I set Q-wp-downspd to be 2m/s.