I've rolled out an update that should fix some of the problems with it deleting things by mistake. It now also has a longer fuse and detonates on impact so it should be easier to land a throw. I've added a few more shop items it can counter to the list too.

From what I'm reading correctly, the code that deals damage to NPCs seems unnecessary if they are ment to be dissolved with env_entity_dissolver, and it is that very damage that players are getting hit by that are causing issues.

Thanks for reporting this, I'll look into it.

On ttt_supercop, if you kill the Supercop with a Zap Grenade he respawns in his normal spawn place and only killing him with the Tau Cannon from the map will permanently take him down. Still, if that's not something you want I can set up a convar for it.

Major Bug Report:

If someone throws the Zap Grenade and it kills a NPC while also hitting the person who threw it, it instantly kills the thrower. It also deletes their body. However, they will not display as dead on the scoreboard and can continue to speak with living players, but are considered as dead for end of round effects.

Is it possible to get a convar for this that disables the vaporizing npcs? This grenade sounds interesting and fun but it instant killing npcs could be an issue on some TTT maps(Ex: TTT_Supercop).

It's a Trouble in Terrorist Town addon that uses the TTT grenade base so it isn't compatible with Sandbox.

is this weapon not available in sandbox, I can't seem to find it anywhere.

Thanks for flagging this up, I've updated it now.

Hey just letting you know the way you overwrote the SWEP:PullPin() function to change the throwing animation causes conflicts with other mods trying to override the same function.

You can easily fix this by overriding the function the proper way using self.Basclass:
function SWEP:PullPin()
self.BaseClass.PullPin(self)
self:SendWeaponAnim(ACT_VM_PULLBACK_HIGH)
end

What this does is just calls the original PullPin() function before making the change you want.