2 Questions: How to make players see mod item and how to stop item from dissapearing?

Hello, I have 2 problems. For some reason, other players can't see the item I'm holding, but I can. Also, there's an item that I made on MCrafter that dissapears in 10 seconds or so, but I didn't change the properties of anything like that. Can somebody help fix this? (I have been desperately wanting to add my mod to an app or popular mod list, but can't do it with all these bugs!)