So, recently I've had the problem that everytime I try to load the last save after quiting hammer every change just doesn't show up. It's like it never happened. This message also shows up.
The invalid brushes are most likely causing your issues. Read up on them here: https://developer.valvesoftware.com/wiki/Invalid_brush Use the Check for Problems tool to find them in your map.
Make sure you aren't making displacements into func_detail, that sometimes gets me and my map will not compile. (Though I'm pretty sure it will tell you in the compile log that you tried to do that)
