I have a situation where HGVs disappear from the network after 60 seconds of waiting time for lane change to turn left. Other vehicles would let them in, but they don't change lanes. Why?

Check if the lane where the HGV wants to change to, is closed to HGVs (button 'Lane Closure...' in the link/connector window) or if the lane change to this lane is banned for HGV (button 'No lane change...' in the link/connector window).