When is it popping off the string? Torque induced by the shooter can cause this. Twist the string and/or torgue the bow and it's likely to happen. Especially when trying to let down.

Also if you have, say, a 70# bow and it's backed off to 60# then there may not be enough tension on the rigging, which can cuse it.

Cam lean is another possibility.

Then again, it could be a combination of any or all of these.