[Please Mark As Closed] Generic Crash - "Watching Server"

Crash Report: https://gist.github.com/willies952002/f9dc8c19be3355af11b3

A friend and I were messing around in the snapshot when we decided to test out the Elytra. So that's we teleported both of us up to 10k and start flying around to see how far we could get. A while into the flight (we had dropped down to around 4,000 blocks) the server crashes with the above report.

I'm wondering what actually caused this and would appreciate all input.

Side Question: the "Is Modded" is reporting as "Unknown", I'm guessing this is because of it being a snapshot build?