There is a leg IK node for that. Move the IK bone in place with a transform, and run the leg IK none after.
And what’s causing it is that you are probably replacing the value to 0,0,0. Turn on show bones, and you’ll see where your IK bone is being placed.
You can play with the setting. Change to Additive for instance (or whatever it is called?).
If you dont have IK bones, then just add them saves you from issues.