Enrolling preview program, factory resets whole console

My suspicion would be the fact that Xbox A is enrolled in the preview program. I had a number of issues (mostly to do with purchasing content) doing this exact thing between my brother and I (problems seemed to go away after he had enrolled.)

Fix #1 - Try to enrol console B in the Preview Program. This may take a few days but to avoid future problems you should definitely enrol.

Fix #2 - Try uninstalling the smallest game title (ex. an arcade title) and reinstalling it while signed into the profile it was purchased with on the opposite console. (try to boot it up at least once before testing with your sons profile.)

LAST RESORT - Fix #3 - Factory reset & reassign home consoles. (to save a whole lot of time downloading, transfer your games to a hard drive before factory resetting)

I hope one of these works for you & keep us updated!

If an Account opted into the preview program for the console but you don't have access to said account any longer, try uninstalling the app from the console through My Games and Apps. If it does not appear there for you, your best bet would be to reset
the console back to factory defaults and start from scratch. That way, the preview program won't install when you reload the console with your account info rather than the account that enrolled in the preview program. Here is a quick How-To for resetting
your console.

http://support.xbox.com/en-US/xbox-one/console/reset-console-to-factory-defaults

Good Luck!

If an Account opted into the preview program for the console but you don't have access to said account any longer, try uninstalling the app from the console through My Games and Apps. If it does not appear there for you, your best bet would be to reset
the console back to factory defaults and start from scratch. That way, the preview program won't install when you reload the console with your account info rather than the account that enrolled in the preview program. Here is a quick How-To for resetting
your console.

http://support.xbox.com/en-US/xbox-one/console/reset-console-to-factory-defaults

Good Luck!

I've tried that. I have fully factory reset the console and logged in with an account that has not signed up for preview. The Dev Mode app still tells me it's still activated.

Is your console by chance enrolled with the Xbox Insider Preview program?

If so, there was an issue with one of the last updates, where the sound wouldn't work.

If you can't reset the sound settings, you have to do a factory reset (keeping your games and apps), and then setting the sound correctly.

If you want to unenroll the console from the preview program here is the whole FAQ and info on how to do that.

https://support.xbox.com/xbox-one/console/xbox-insider-program

You may want to try a factory reset keeping games and apps, Or a complete factory reset so the console is totally wiped and refreshed and just download your games again.