I had this bug too in the old days..
It usually means you've got to many entities in one place or have reached the maximum amount of entities and texture limits / and or model limits per map.
In that instance I separated my map into 2 sometimes even 3 pieces aka maps. I never experienced this problem again when I upgraded to these compilers :https://twhl.info/thread/view/17830Be advised:
These compilers will most likely break most your maps as they're much more accurate than the ones you might be using right now. They find leaks the older compilers wouldn't have found. Anyway it'll just help to make your maps even better so don't worry about it. In either case they provide much greater model and texture caches in Megabyte for any map to use. That alone makes it worth it.
Not to mention couple new entities - faster map compiling, or better light and shadow settings. Things that are making your maps look even greater than before.