My power brick shuts off after loading a game by couple of minutes

Was able to fix it by shutting down the xbox and unplugging the power brick for a couple minutes.

Is your console in instant on or power saver mode. Switch it to the one it's not set to and hold the power button on the front of the console until it shuts off. After it shuts off unplug the power brick from the console and the outlet for a minute press
the power button the console 3 times after a minute plug everything back in and power back on and see if the issue is resolved.

According to bungie.net you need to do a full shutdown if you get this error.

Press and hold power button for about 10 seconds until console shuts down.

When light on power brick is orange disconnect the power for a couple of minutes.

After a couple of minutes switch back on and try again.

I'm in the preview and my external HDD still works with no problems.

What make and model is your HDD?

I just looked in the preview forums and can see a couple threads about USB HDD's no longer being detected after the 1407 update.

A hard power reset fixed the problem on one of the threads.

Press the power button for about 5 seconds until console shuts down. Once console has fully shut down and light on power brick turns orange you should disconnect the power for a couple of minutes.

After a couple of minutes switch on and try again

Over the years I've seen the suggestions of

Go to settings/devices & connections/blu ray. Then clear persistent storage.

Uninstall and reinstall the blu ray app.

Hold down the power button on the front of the console for ten seconds. Wait for everything to turn off. Once everything has shut down for a couple of minutes unplug the cord from the back of the power brick. Wait another couple of minutes, reconnect
the cord to the back of the power brick. Press the power button on the front of the xbox.