When a magazine is spawned to a weapon through the MuzzleComponent magazine template the InventoryItemComponent::OnParentSlotChanged invokes but the new slot argument has no data populated.
SCRIPT : {0A84AA5A3884176F}Prefabs/Weapons/Magazines/Magazine_545x39_AK_30rnd_Last_5Tracer.et
SCRIPT : -1
SCRIPT : MuzzleComponent<0x000001E407E80510>
SCRIPT : NULLOptics of UGL however seem to work just fine
SCRIPT : {1ABABE3551512B0A}Prefabs/Weapons/Attachments/Underbarrel/UGL_GP25.et
SCRIPT : 1
SCRIPT : AttachmentSlotComponent<0x000001E466296C10>
SCRIPT : SCR_WeaponAttachmentsStorageComponent<0x000001E4006541E0>The event args should be fixed to return the correct data.