So when I'm on approach for an airport with LNAV and VNAV active and i hit the final STAR i go to click my APP button to begin following the G/S. When i do this in around 2 seconds the cockpit lights fade and the autopilot turns off and the master caution light shows IRS. During this time the F/O displays turn off.
During set up the IRS was aligned and the position was set to current.
AIRCRAFT - Zibo Mod 737-800