I may have missed it, but I didn't see any comment on holding wheel brake as the tow plane takes out slack. If the slack is taken out too rapidly it will jerk the glider, leaving a slack rope. Most contest tows will proceed immediately after slack is out, but if the tow pilot holds for any reason, the slack line will jerk the glider and this may result in some of the problems discussed. My wheel brake is on the spoilers and I don't like unlocking them, but I have reluctantly adopted the "hold the wheel brake" procedure to prevent starting with a slack line.
Hope this helps,
JJ