For the first time in my life I heard a 1st person story of a release failure.
The story follows:

The glider, an ASK-21, was jerked forward by the tug so the front wheel rolled over the rope at the start of an aero tow. The slack was then taken out and the tow was launched without inspecting the hook and release. The working theory is that this somehow cocked the ring set in the hook so it failed to release even with pilot and passenger pulling on the release knobs. The pilot eventually got a successful release by yawing the glider strongly.

AFAIK, the hook in question had not reached it's 2000 tow life limit nor is there any history of repair or maintenance in the hook area. There had been cases where a commercial operator had insisted on providing tows using a chain link instead of a Tost ring set. We think it possible this had damaged the hook in some way.

Operationally, should a roll-over happen again, we will release the rope and re-attach before proceeding with a launch. The release will get special attention in the annual inspection later this month. No chain links will be allowed for any purpose.