ARC9 encountered unregistered PhysBulletModel 'models/Items/AR2_Grenade.mdl'!
We will register and refresh this model for all clients, but this is network-intensive!

Please tell the addon developer to register the model in a shared lua file like so: ARC9:RegisterPhysBulletModel("models/Items/AR2_Grenade.mdl")

I've use Morthalza-90 then that console tell me it has unregistered PhysBulletModel from AR2_Grenade.mdl

I can't tell this is your or something else on workshop so...
I am trying to help to see why this occur then I'll head back to my original game.