i used to get a jamming feeling when i front squatted ATG.
in time... i realized that i was getting some anterior femoral glide (the head of the femur was grinding against the pelvis socket).
i discovered that some of the smaller gluteal muscles have a stabilization function (they help pull the head of the femur back so it doesn't jam in front).
x-band walks. get the medial glutes working.
step ups. pretty high step. trying to do these really very much like a squat (leg high enough so i'm breaking parallel if you get what i mean and really focusing on pulling myself up with my raised leg rather than pushing myself up from my grounded leg).
the step ups (particularly holding weight) got some tiny stabilizers that lie under the glute max firing (don't let your knee cave in!).
i haven't had a problem with anterior femoral glide since then.