Laptop heating up and dying in my backpack

We've been seeing this with some of my organization's Macs.

There are several possibilities:

• Bad Lid Angle Sensor (2019+ models), or sleep sensor (2018 and earlier)
• Some app(s) are not allowing the laptop to go to sleep.
• Laptop is waking up. There are multiple reasons.
  • A key has been pressed, or the Trackpad has been pressed.
  • The display lid has opened slightly.
  • An external device has been connected or even disconnected.
  • macOS may wake on its own to do some processing.

You can easily test the Lid Angle Sensor or Sleep Sensor by closing the lid & waiting a few minutes. Then very slowly open the lid just a little bit. The display should be dark until it opens about the width of a pencil where you should see the display turn on. You should see the login prompt.

You can try to manually put the laptop to sleep by using the "Sleep" option on the Apple menu. However, if the Lid Angle Sensor is misaligned, then this may not work. This should work if the laptop uses a sleep sensor instead.

Maybe try logging out first before closing the lid. See if this makes any difference.

Have you tried a complete "Shut Down" of the laptop to see if it remains off?

Make sure you disconnect all external devices prior to putting the laptop to sleep or power off the laptop, otherwise you will end up waking/powering on the laptop.