I had problems to get the correct state of the autopilot vvi. AP_VVI_armed is probably coresponding to the dataref .../vvi_status, which is a integer value (0,1,2).
AP_VVI_armed didn't work correct until I added v=2 to the AP_VVI_armed. So inside SimVim AP_VVI_armed seems to be an integer and not a boolean value. Accordung to the dataref documentation v=1 (armed) is no longer used, only v=2 (captured) ist a possible value