So it looks like you're shooting a laser shot right at the flags, which definitely has enough force to turn them.
However, the shot is angled at a steep angle up, which means only a fraction of the velocity of the ball- the horizontal component- is actually being used to turn the flags.
Also, the shot hits the very inside part of the flag in the video you linked, which gives you a lot less leverage. If you aim at the outer edge and straighten out the shot angle, that should help turn the flags much more easily. This will become a lot easier with v5 vision sensors once they're out.
I know vex said they did some pretty extensive testing on the detents wearing out, it sounds like the flags don't lose or gain much stiffness even when they're turned back and forth thousands of times. However, there's definitely some variation between different flags just because of manufacturing tolerances etc. Is it possible your practice field flags were just easier to turn?
If you get a chance before your next competition, try to level out your shot angle and aim for the outer edge of the flags. Good luck!