What? I wrote a description here, why didn't it post properly? Well I can't copy the entire thing from memory but the gist is that on 19.2 forge the Y value for vertical slabs on create contraptions gets inverted. So if there is a vertical slab at 400, 60, 300, it will complain that there is immovable deepslate at 400, -60, 300. I had more information in my original post but I guess github just decided to delete it.
What? I wrote a description here, why didn't it post properly? Well I can't copy the entire thing from memory but the gist is that on 19.2 forge the Y value for vertical slabs on create contraptions gets inverted. So if there is a vertical slab at 400, 60, 300, it will complain that there is immovable deepslate at 400, -60, 300. I had more information in my original post but I guess github just decided to delete it.