Quickly Closing 2 Games in the guide menu will force me back to the main guide menu without...

You can't use the Main Dashboard, when playing a game.. You have to use the Guide Menu, when you press the Guide Button in center of the controller (The one with the light etc)..

If you want to exit a game, after saving & not turn the console off.. Press the Guide button & select Menu on the page that pops up & it will close the game & take you to the Main Dashboard..

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If the game wouldn't allow you to quit to the main menu you could have just went back into the dashboard by taking the disc out, select the option from the guide menu, or reset your console.

I've had this as well. Press the guide button on your Xbox and wait for the menu to open. Once I do that and then close the guide, it unfreezes for me.

Well it's officially no longer a Preview Program issue.

I completely unenrolled from the Preview Program and performed yet another factory reset. Everything worked perfectly for a couple of days. I hear the "chime" noise when I hold the guide button, I can smoothly go between menus, everything worked great. Until
I started reinstalling all my games and Rock Band 4 DLC. Particularly while the Rock Band 4 DLC was installing (several hundred files, I should say) and I'm getting all the notifications about each song being ready to play after they're installed, I noticed
the lag came back. It's taking a good 30-45 seconds for my "What do you want to do?" menu to pop up and the "chime" noise that goes along with it is gone. Menus are laggy. I press down several times in the guide to get to an option at the bottom of the screen
and it'll freeze for a second, before jumping down there suddenly.

I'm really at a loss here. The console seems to work fine until I start installing things. And yet, everything is installed to my external, and I have the same problem when my external is unplugged from it.

Since you're a member of the Xbox One preview program, please be sure to report any issues you come across using the Feedback app and then post on our Preview
Program forums for further assistance from the proper folks.

Thanks!