I've tested the following mobs:

• Cave Spider
• Spider
• Creeper
• Zombie
• Guardian

The trident disappears when you hit a mob. If it misses and hits the ground it returns like normal.

Steps to reproduce:

1. Create creative world in 20w10a.
2. Give yourself a trident and enchant it with Loyalty (level doesn't matter).
3. Spawn a mob, throw it and hit the mob.
4. The trident will now be gone.