Both wireless controllers have lost sync at same time

I had a problem with this too, i learned it helps to connect your wireless controller after you connect the wireless reciever by pressing and holding the sync buttons on both the xbox and wireless controller at the same time. Just first plug in and connect
to your wireless reciever. then turn on your wireless controllers, then quickly press both sync buttons on your xbox and controller simultaneously until it connects. other then this i have searched and not found another solution, but i hope this helps

Updates:

Paired both controllers to console at the same time. Both controllers lost and regain sync at the same time.

Paired Elite controller to iPhone. No disconnects.

Paired one controller to console and other to phone. Controller connected to console disconnected, controller connected to iPhone stayed connected.

The wired pads are up to £25 where as the receiver is only £15.

Its works just the same as the Xbox, just sync the pad to wireless receiver holding the button on the pad and the button on the wireless receiver.

Controllers can only be synced to either the xbox or wireless receiver at a time. The controller cannot be synced to both.

No confusion

I had a similar issue with one of my controllers recently. Try holding the sync buttons on both the controller and console at the same time until the wireless controller reconnects.

The sync button on the controller can be found at the front and the sync button on the console is on the left hand side just in front of the USB port.

To sync a controller to the Xbox you have to press the sync button on both the controller and the console. If you haven't done that, then it will not sync up. Instructions can be found here

https://beta.support.xbox.com/help/hardware-network/controller/connect-a-wireless-controller.