this has happened to me quite a few times, i was fighting and my sword duplicated and deleted the bow in my inventory, when i clicked on the 2nd sword it dissolved aswell and i never got my bow back, so after making a new bow i put my sword in my hotbar to prevent it from happening again, except this the same thing happened with my sword, it got overwritten by my axe, its pretty frustrating too since both times the items were all maxed out and now theyre just gone

I just lost my dank null to this as well, the slot containing the dank was locked (Inventory profile feature) which might have something to do with it?

You have a mod that is checking your main hand, for me this was sophisticated backpacks with the feeding upgrade, if you need an alternative use feeder upgrade helmet.