So I played around in the new snapshot 18w14a and noticed the trident with the riptide from what I heard was going to be changed and when I tested it I lost the trident when I was in the water non-creative mode.
I don't think that was supposed to be intended to loose it since the loyalty enchantment won't work with but I came up with this idea, instead of the riptide being a one time use item maybe you can make it still usable when thrown you will go along with it instead. I mean that would make since if you throw a trident you shouldn't loose it since it will be going along side with you.