I always have a hard time bracing my lead leg when I land. Are there any drills or “cues” to help me keep my lead leg braced?
is from Steven’s blog might be useful for you.
Not bracing the front leg can also come from your hips being closed at foot plant. When you land, your hips want to open and rotate which pushes your front knee forward some. Looking at your video you put up in another post was inconclusive from the angle and quality of video. Try taking some video of you pitching from a side view and see if your hips are open at foot plant.