leaf saws are tricky and possibly one of the most annoying and hard to diagnose errors in goldsource editing(imo). the best way to combat them is to backup your work
often so you can just go back if you can't find the problem. (I notice you said you went a few steps back, but maybe you didn't go back far enough before the leaf-saws were occuring)
Here are some other things you might try or keep in mind for leaf saws (if you still can't fix it upload the map and i'll look at it for you if you like):
--"Warning: Leaf portals saw into leaf
Problem at portal between leaves 477 and 502:
(-150.000 -1890.400 320.000)
(-166.131 -1877.598 -64.070)
(-166.052 -1877.558 -64.070)
(-165.957 -1877.515 -64.000):" ERROR:
Caused by a bad brush, whether you or Hammer did it, lol! = )
A good portion of the time, this error comes up erroneously, sometimes on even the simplest architecture, inexplicably. These dreaded Leaf-saw errors are interrelated to many other errors in Hammer compile, which makes them especially infuriating and hard to diagnose and quantify.
Disappearing Brushes and HOM can be the cause of a single one of these "leaf-saw" errors. Multiple Coplanar errors (Coplanar Plane errors on every brush in your map) can be caused by one leaf-saw error. If you have a problem in your map, check the compile log... there is probably a "leaf-saw" error!
These Errors alone are the reason I constantly back up my levels. They can cause your whole map to be uncompilable and/or extremely difficult to find the problem.
FIXES:
-VIS -full. Many "leaf-saws" that come up in FAST and NORMAL VIS will disappear in FULL.
-copy/paste method. copy the whole map into a new .rmf file, recompile.
-Func_walling. Find the bad brush or brushes and make them func_walls (make them illusionaries if you have a tight clipnode budjet).
-revert to an earlier, error-free version
-eliminate any structures/brushes outside the compilable area of your map (even if they are nulled they can still possibly cause this and other problems).
-sometimes rotating multiple complex objects causes this error, especially using "ctrl-m" to move them. Try shift-rotating instead, or rotating less objects at a time.
-Some other errors may erroneously cause leaf-saw errors. Make sure there aren't any other "problems" with your map you might be overlooking!
-The simplest, most innocent looking structure can potentially be the culprit of your leaf-saw error, and can erroneously spawn additional leaf-saw errors. A lot of time working fast in hammer you can alter a brush VMing without even realizing you have with one slip of the mouse! Find the culprit brush and kill it!
-If none of this helps, divide your map into quadrants and temporarily delete sections, then compile and see if the error comes up (ctrl-z to undelete ok parts, or export to another map). once you've narrowed it down to one quarter of the map, it should be a lot easier to find the bad brush or brushes.