Hello all, long time reader, first time poster.  I just bought the Carenado Phenom 300 since it was on sale and have two issues I wonder if anyone else has had.  

1.  Autopilot will not capture target altitude.  Just blows right by it up or down.

2.  Periodically the engines just shut off.  No buttons being pressed, just shut down.  I can restart them easy enough but it is obviously not right.

Thanks in advance for any help.

Ok, so I figured out #2.  I am dumb.  I have a rotary assigned to mixture on my X-55 throttle and it was causing the cut off switches to cut off.

ok, need more info for target altitude issue.

After selecting the target altitude, do you select "VS" and set a rate of decent or ascent? You should see a White "ALTS" displayed and green "VS XXXXFPM". on your PFD.

If you don't get the ALTS, rotate the alt sel knob again until your requested altitude is displayed.

I fly mostly the P3D version but started with the Boxed FSX 100 then the 300.