Aircraft descends when switching to Althold mode

Hello everyone.
I am currently building a helicopter drone with a jet engine.
As for the question, it is elementary.

The aircraft is raised in “Stabilize mode” and then switched to “Althold mode” to lower the swash plate to the minimum location and lower the aircraft.

Please let me know what the problem is, whether it is a problem with the setup of the aircraft or whether it requires a detailed configuration.

Best regards.

Hi @itagaki-jetset , post a log please.