After throwing a trident, at least one with Loyalty III and Channeling I enchantments, there is a bug where you can't use your shield anymore. It seems to be indefinite, and the only reliable solutions I found were to reload the world, eat/drink, or use a bow/crossbow/fishing rod. This glitch happens everytime I throw my trident and it returns to me, even if my shield is unequipped before I throw the trident.