I would check the trigger guard plunger and plunger spring to insure it is moving out the full amount. If it is not then it isn't holding the trigger guard tight enough to the frame. Check the trigger guard plunger to make sure it is not malformed and not correctly mating with the frame correctly.
Also, while everything is apart, where you can look into the frame, see how the plunger is mating with the frame when you put the trigger group back in. When in place the plunger should extend fully into the frame. Also check the area where the plunger goes into the frame to insure that no one has modified that cut out where the plunger goes to make it easier to snap the trigger group back in. I have seen people do this because they thought it was too hard to put the trigger group back in. It should not go in super easily, it should be a good snug fit.