That's because your first checking there is a collision and then setting the x,y coordinates. and then you're checking for another collision, which is almost certainly going to fail and thus that variable will be set to 1.
if (place_meeting(x,y,Collision))
{
x = random(room_width);
y = random(room_height);
}
else
{
AI_stage = 1;
AI_timer_neu = 0;
}