I just updated my server to Spigot 1.10 yesterday, and was checking the console logs for errors this morning to make sure everything was working OK. I noticed this stack trace was being spammed to the console at one point.

[02:24:00] [Server thread/ERROR]: Could not pass event PlayerMoveEvent to Serenity v1.10.0
org.bukkit.event.EventException
at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:310) ~[spigot-1.10.jar:git-Spigot-c55900f-9af379f]
at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:62) ~[spigot-1.10.jar:git-Spigot-c55900f-9af379f]
at org.bukkit.plugin.SimplePluginManager.fireEvent(SimplePluginManager.java:502) [spigot-1.10.jar:git-Spigot-c55900f-9af379f]
at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:487) [spigot-1.10.jar:git-Spigot-c55900f-9af379f]
at net.minecraft.server.v1_10_R1.PlayerConnection.a(PlayerConnection.java:610) [spigot-1.10.jar:git-Spigot-c55900f-9af379f]
at net.minecraft.server.v1_10_R1.PacketPlayInFlying.a(SourceFile:126) [spigot-1.10.jar:git-Spigot-c55900f-9af379f]
at net.minecraft.server.v1_10_R1.PacketPlayInFlying$PacketPlayInPosition.a(SourceFile:57) [spigot-1.10.jar:git-Spigot-c55900f-9af379f]
at net.minecraft.server.v1_10_R1.PlayerConnectionUtils$1.run(SourceFile:13) [spigot-1.10.jar:git-Spigot-c55900f-9af379f]
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [?:1.8.0_66]
at java.util.concurrent.FutureTask.run(FutureTask.java:266) [?:1.8.0_66]
at net.minecraft.server.v1_10_R1.SystemUtils.a(SourceFile:45) [spigot-1.10.jar:git-Spigot-c55900f-9af379f]
at net.minecraft.server.v1_10_R1.MinecraftServer.D(MinecraftServer.java:733) [spigot-1.10.jar:git-Spigot-c55900f-9af379f]
at net.minecraft.server.v1_10_R1.DedicatedServer.D(DedicatedServer.java:399) [spigot-1.10.jar:git-Spigot-c55900f-9af379f]
at net.minecraft.server.v1_10_R1.MinecraftServer.C(MinecraftServer.java:672) [spigot-1.10.jar:git-Spigot-c55900f-9af379f]
at net.minecraft.server.v1_10_R1.MinecraftServer.run(MinecraftServer.java:571) [spigot-1.10.jar:git-Spigot-c55900f-9af379f]
at java.lang.Thread.run(Thread.java:745) [?:1.8.0_66]
Caused by: java.lang.ArrayIndexOutOfBoundsException

It seems the event never reached my plugin so I don't think there was an issue there. I do have a registered listener for the PlayerMoveEvent, but again it seems to throw the error before executing my listener code.

I have an idea what was happening when this occurred. Some players on my server built an elytra launcher. They have about a 100 boats placed on one tile, and you jump, start gliding, and clip the edge of the boats. The pushback from the boats causes you to fly really really fast (you can reach Y 400 from sea level). Based on the chat it seems one player was trying to use that when the error occurred. So it seems to be related either to elytra gliding, or moving really fast, or both in combination. Once she stopped trying to use the launcher, the error spam stopped.