I could look into the changes that were made. I can compare the code posted in update 3 and the changes made. For this it is very convenient to use Meld (Linux/Windows) or Winmerge (Windows). Meld is my favorite.
https://sourceforge.net/projects/meld-installer/
After the new year I will install VC6.
If the monsters use cluster grenades, then the algorithm will have to be supplemented. Since it now removes damage when friendlyfire is disabled in the co-op for the game completely. Except for the player who fired the grenade. The damage works on him.. Damage also works in the singleplayer at the "easy" difficulty level. At this difficulty level, can also disable damage in a single player.
UPD:
It looks like there are no monsters that use cluster grenades. This is good. This means there is no need to change the algorithm