I have recently come across a strange issue with my map in Hammer. For my map, I've boxed it all up inside a sky box, making sure there were no leaks anywhere on the map. However, Hammer would freeze up when trying to run my map. Strangely, if I remove a piece of the sky box, like the ceiling, the map will run just fine. I have no idea what the issue is and have not found every solution to fix it.