Startbutton xbox one controller

First thing to try is a simple
power cycle on your Xbox. I could recall a couple of rare occasions where the buttons would act weird, and doing to steps above will fix it.

Go to the “Xbox Accessories” app and see if you can
reset the controller to default settings. Maybe some button mapping got corrupted?

Also
check for a firmware update on your controller. This will reset the controller and update it to the latest firmware.

Is the button dirty, or does it stick when pressed? With the controller turned off and the batteries removed, try swabbing around the button (with a Q-tip) with some rubbing alcohol to clean it. See if that helps anything.

Worst case scenario, the button may be defective, and will need to be serviced by Microsoft. Set up a repair by going
here, or contacting Xbox support for more help (choose phone or chat).

I experienced the same problem.

Played for about 4h, got back to the mainmenu of Diablo 3 to adjust some settings, returned to startscreen and after pushing the startbutton I was asked to adjust the screensize again. (Like when you first start the game)

Everything was gone and I had to create a new character.

I read in other forums that many people are experiencing the same problem.

And you can't even copy your savefile to an USB Drive or the Cloud because it's blocked, you can just move it.

Is this an Xbox One controller, or an Xbox 360 controller? If it's an Xbox One controller, are you connecting wirelessly to the PC via Bluetooth, or with the Xbox Wireless Adapter?

Xbox one controller with an xbox wireless adapter

Check these support links for a solution:

Connect the Xbox Adaptive Controller to Xbox One

Connect the Xbox Adaptive Controller to a PC

Well what kind of controller is this is it the original Xbox one controller or 3.5mm controller? If it is the original Xbox one controller it might be the controller malfunctioning with your Xbox because they are outdated.