Just took a look at my Shield Plus, and didn't have that issue.
Does the lower trigger (safety blade) have good resistance and springiness when you press on it and let go? If not, maybe the plastic tip that gives it resistance is broken.
If the resistance is OK, does the plastic tip on the back of the lower trigger stick out far enough to make contact with the frame? If you used your finger nails to move the upper trigger without touching the lower trigger (safety blade), does that plastic tip make good contact? If not, maybe that little tip got damaged and shortened. Or maybe the trigger assembly isn't seated very well inside the frame. I'll post some pictures.
This is the trigger for the Shield 2.0, should be similar except in the Plus the lower trigger (2) sits inside the middle of the upper trigger (1), instead of hanging below. There is a tiny pin (3) that holds them together. The red rectangle is the little piece of plastic that rotates forward and resists the lower trigger from rotating backwards, with the pin acting as a as a fulcrum. The blue rectangle is the little plastic tip that catches the frame if the lower trigger doesn't rotate.
OK i just saw your vid