Have you found a solution to this problem? Excessive chain wear will cause the entire gripper to twist when the cam follower contacts the cam, even if the gripper opens, it may not be opening enough for sheets to grab. If that is the case then you could try to add some tension to the chains via the springs near the delivery end just to get by but the chains will need to be replaced to fix the problem
The only qm with 4 grippers is the qmdi, a qm 2 color has 3 grippers but the 2 deliveries are identical otherwise. Check the integrity of the rubber pads under the gripper fingers , and look for wear or glazing, clean with alcohol.
There are 3 bolts on the gear of the gripper shaft on OS to adjust overall timing, and this may need to be checked and adjusted after a bad jam.. GOOD LUCK