I'm not sure why this doesn't work.
In the attached cap, the grey skeletons have MoveType=1, while the red skeletons have MoveType=2. MoveType=1 means they'll walk till they reach the end of the platform, then turn around. MoveType=2 means that it'll only turn around once it hits a wall (I've given the red skeleton gravity=0 for floating purposes).
Use "Destroy on startup" to delete all the grey skeletons, and the red ones work perfectly. Do the same for the red skeletons, and the grey ones work perfectly. Have both in the same sheet, and they start glitching out.