Check for a loose Zone 2 speaker wire strand touching another speaker post either at the AVR or the Zone 2 speakers.
If still no joy, there is a lot of helpful information provided in posts 1-8 of the 2015 Denon AVR Owner's thread which is where questions regarding the X4200W are discussed. Refer to post #5 in that thread for the various resets to try.
The "OFFICIAL" 2015 Denon "S-series" / "X-series" AVR Owner's thread + FAQ (HDCP 2.2) | AVS Forum
If still no joy, there is a lot of helpful information provided in posts 1-8 of the 2015 Denon AVR Owner's thread which is where questions regarding the X4200W are discussed. Refer to post #5 in that thread for the various resets to try.
The "OFFICIAL" 2015 Denon "S-series" / "X-series" AVR Owner's thread + FAQ (HDCP 2.2) | AVS Forum