iPad locks itself and requires passcode after exiting power off menu

An iPad with configured TouchID, or FaceID, will still prompt for a device Passcode in certain circumstances.

Whilst not an exhaustive list of conditions, you will be prompted for a Passcode:

• after a defined period of inactivity
• after concurrent failure to successfully unlock using TouchID/FaceID
• if the Sleep/Wake button is rapidly pressed five times (this intentionality disables biometric authentication)

It should be noted that reversion to requiring a Passcode is a deliberate feature of the iOS/iPadOS security architecture. The TouchID/FaceID interface is intended to provide a quick and convenient method to authenticate when the device is being used regularly by the principal user of the device; biometric authentication is not a replacement for the primary device authenticator - this being the device Passcode.

I hope this clarification is helpful to you.

If iPad isn’t responding, do one of the following:

• On an iPad with a Home button: Press and hold the top button and the Home button at the same time. When the Apple logo appears, release both buttons.
• On an iPad with Face ID: Press and quickly release the volume up button, press and quickly release the volume down button, then press and hold the top button. When the Apple logo appears, release the button.

If your iPad doesn’t turn on, or if it gets stuck during start up, see the Apple Support article If your iPhone, iPad, or iPod touch won’t turn on or is frozen.