I have no idea, could you provide a very simple capx?
I guess that, the issue might come from platform behavior with (soiled) ground, since platform behavior will change the position too.
rex_moveTo behavior: fix the behavior of "push out solid".
Please updates that new version of rex_moveTo behavior. Now the sprite will not have x shift when stop by solid. Tested by @99Instances2Go 's sample capx.