Originally Posted by Corse-R

Happens when you don't have enough care with the boards and you have your upper rear arm in the longest position, the turnbuckle doesn't grabs enough (posionous by nature, because is the weakest a-arm lenght).

Exchanged them for a pair I had from a old Tamiya car in 3x24mm long (1mm longer on each side). Solved the problem. As a plus, I have an hex to grab rather than a silly hole.

If you managed to bash the arm, better to exchange for a new one, much probably you stripped the threads created on the plastic and now will not grip enough hard. Also, try the longer turnbuckle trick I did and give it to the a-arm one or two turns more than the ball cup this gives a try to make it stiffer.