with RC1 on Pixhawk-Mini I have the same.
https://discuss.ardupilot.org/t/copter-3-6-0-rc1-available-for-beta-testing/28285/8
Maybe its related to this
https://discuss.ardupilot.org/t/copter-3-6-0-rc1-available-for-beta-testing/28285/36
I guess the dev team know that issue