I might be being obtuse and not seeing something but your inventory system shouldn’t have any effect on your weapon collisions. They are distinct pieces are the overall system and shouldn’t inter-mix. Otherwise you lose your modularity of the game system.
Your inventory tells you what items you have. The weapon collision is part of the game combat system. Maybe try starting a test project without any inventory system just the bare bones of what you need to build your combat system. Whenever I start work on a particular system I always use a test project to design it seperate from any other system if possible. That way I am only dealing with issues in that particular system.