auto lock

Ensure that you have not enabled Low Power Mode, as doing so will override many iPad settings - including setting/locking Auto-Lock settings to 2 minutes.

Settings > Battery > Low Power Mode - set to OFF

After checking that you have not enabled low-power mode, perform a forced restart of your iPad:

• 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 other iPad models: 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.

Try a reboot => Force restart iPad - Apple Support

If you don’t see the Low Power mode, ensure that you have performed the previously outlined forced-restart procedure.