I've had rope breaks, weak link break, with slack line during training. At altitude so not an issue.
I have had ropes part on takeoff, normally at the initial strain on the takeoff acceleration, far up the rope, so it was missed on the first rope preflight of the day and failed late in the day. The glider hade barely moved 50ft, so it was not an issue.

I've watched one ply of a three ply poly part about 50 ft in front of the glider. After I got off tow at altitude, I told the tow pilot he would need a new rope for the next tow.

If your TOST released the ring, either it was not hooked up correctly, did it rattle after hooked up?, or your TOST springs are getting weak. Time to replace it.

BillT