If you can isolate which side it's sticking on, that'll help. Do you see signs of it dragging anywhere, on the frame or the slide? Take the right side off (as you're looking at it from behind the gun) and see if it still sticks on the left.
If it's not dragging anywhere, there could be a problem with the pin in the plunger, or the spring could be hanging up somewhere in the tube. Take those out, carefully, as they'll fly across the room, and inspect them. The spring isn't supposed to be a very heavy one. Check the thumb safety plunger for any rough spots. Put both sides of the thumb safety back on without the plunger tube springs and pins.
Does it flip up and down with no resistence? If not, locate the resistence as it drags across the frame or receiver somewhere. Nothing? Likely at this point the problem is with the contour of the shoulder where the plunger engages it. It's probably at too radical a radius. Not much can be done for that, if it's the cause. You could try to re-work the radius with a file. Better option is to let the company fix it.