Althold and loiter mode not working

I made hexacopter using Pixhawk 2.4.8. all the propellors and motors are in correct direction. it’s working fine in stable mode. but while I use Alt hold mode it lifts about 10-15cm and goes into one direction and got crash, without following my commands. when it’s lift in the air it doesn’t follows my instructions in Alt hold mode.

I hope you are okay and nothing happen to you, think positively, at least you are still in one piece and without injury writing this post.
If you are using ArduPilot flight stack with the supported flight controller unit, See if this guide help you in your next adventure journey.