The bug
In multiplayer when repeatedly using a trident, with the Riptide enchantment in the rain you can be kicked for flying. As flying with a trident appears to be an intended feature, the anti-cheat should probably not kick players using Riptide to fly in the rain.
How to reproduce
Here is a video on how to reproduce: https://www.youtube.com/watch?v=42zHOvA6gVA