Regarding the grenade launcher's projectiles sometimes bouncing off enemies in the N64 game, that rang a bell with me, but I can't find any reference to it in the official Wiki. The only reference I've been able to find is this:
"
Enemies can be activated, as I call it. By that I mean that sometimes you see
some part of an enemy (e.g. its left arm, left leg and some of its head)
without him realizing you're there. In this case your autoaim won't work and
grenades will simply bounce off them instead of blowing up on contact.
Sometimes even a direct hit doesn't damage them. To stop this, just run into
his sight to activate him. Once he has seen you he can never return to the
inactivated status. This is extremely useful to keep in mind when you want to
lob grenades around corners or when you know that there are mutants in a
basin in front of you. Just dive down briefly, surface and leave the water.
Now you can fire a few grenades into the water and see the blood fly all
around. If you manage to hit an inactivated enemy, he is also activated."
I could be wrong here, since it's been a long time since I played DN64, but I think this was a very rare occurrence, though I don't remember if it always happened at the same few specific points in the game, or if it was more random. I do know that most enemies, if 'inactive' will become active when you use a weapon or explosive on them, as you'd expect, and the fact that I can't find more information about this would seem to suggest that it's not a common problem amongst DN64 players.
Source: I can't link directly to the page, as it's against Gamefaqs' rules, so go to:
https://gamefaqs.gam...e-nukem-64/faqs
and the above quoted text is in the FAQ by
KeeperBvK, so thanks to him/her for documenting it.