The Approach hold mode is crashing my plane

I recently moved into larger aircraft in fs9( I was using fs10 since I was a kid but transitioned to fs9).Once,I was flying a default Boeing 777-200 in cruising altitude at 30,000ft ASL. The cruising speed was set and the autopilot properly configured(I think so😎).I thought to experiment a little so I switched on the APPR mode(I know that it is used for landing procedures) and once i did that the plane did an erratic nose dive!😱

It was almost impossible to recover since i was going in 16x simrate🤯(I managed to switch it to 1x).I found out that even the ALT mode was set the autopilot is not responsive.Soon,I got overspeed warnings too.At this time I had pulled the joystick all the way back but no response.Then I realized that the autopilot was on,so I disengaged and applied full power and climbed back to cruising altitude.Then I was thinking,"what the hell just happened?"🤨

I normally refrained from activating the APPR in all phases of flight,since then, and I used NAV mode(in GPS) or manual control for my approaches.But recently I was doing an ILS approach in a Boeing 737-400 so I was expecting that the APPR(approach Hold mode) would fly me to the runway threshhold so I can solely focus on power and flaring.At 3000ft with ILS frequency set and glideslope alive I activated the APPR but the same incident happened and this time the plane crashed and spoled my whole flight!!

*Can someone explain me what is going on? Is my time of APPR activation not correct?Or is something wrong with my computer? certainly I have not tried this in a Cessna(Im not a regular simmer though).
Everyhing is working fine except the APPR mode- which spoils my flight everytime i use that.🤦‍♂️🤷‍♂️