So, there's a little bug in hammer which makes overlays completely transparent, and I'm here to tell you how to fix it. This bug makes the overlay texture disappear, therefore taking some time away from mapmaking (just a tiny bit though). This bug is usually caused by cutting the brush the overlay was on, and this could be very problematic if you are making cliffs, small details, or splitting textures between one brush. One way to avoid this bug is re-assigning the overlay to the brush it was originally on. Anyways, that concludes this guide, please reply to me what you think!