Please help me Pixhawk hexacopter unstable problem

ArduCopter
1

I want to ask two questions.
I set the hexacopter 1500 size drone as the latest arducopter.
We changed the PID value under three conditions.

Changed PID settings for the Hexacopter 1500 drone.

  1. I tried autotune in althold mode.
    -> stabilize mode: stable
    -> althold mode: stable
    -> Loiter mode: Unstable, drone roll vibration is severe.

  2. I tried autotune in Loiter mode.
    -> stabilize mode: stable
    -> althold mode: stable
    -> Loiter mode: stable

First, why is it unstable in Loiter mode when you try althold autotune on step 1?

Second, why was it stable in Loiter mode when trying Loiter autotune in step 2?