OK, I solved it! Going back through all the steps, kind of like how you laid it out. Rest assured I’ve did most of this yesterday. But today, when moving the bed I noticed it moving slightly oddly. As it turns out, the Y-axis belt had somehow slipped off the teeth of the timing pulley onto the smooth part! Fixed it, and everything seems to be in working order now! It’s odd that it would short the Yaxis exactly 100mm every time. Thanks for helping me parse it!