In combat mode, item with an infused spell from Iron's Spells and Spellbooks disappears when used.

[Art1xs]

To clarify, it disappears when you use the spell infused with the item or tool (right click)

[Jackiecrazy]

This usually means the item crashed halfway through the hand swap and Minecraft suppressed the error by interrupting the rest of the process. There should be something about it in the logs. I myself have dual wielded infused items without this issue.