Minecraft version: 1.12.2
Wizardry version: 4.2.1
Environment: Server

Issue details: Whenever someone tries to cast a spell, it kicks all the players on the server. In single player it does work but I get the same error in the logs.

Other mods involved: [only list mods that are relevant to the problem]

Link to crash report (if applicable): [give a link to the crash report on gist, pastebin, etc.]

Singleplayer log: https://gist.github.com/MCEventHorizon/c8c68937f4b8fda1fbc76b145f908364
Server log: https://gist.github.com/MCEventHorizon/e5543ea2191127a0c584c18d6c29ed55

I think this part is relevant so I will paste it from the logs:

io.netty.handler.codec.DecoderException: java.lang.IndexOutOfBoundsException: readerIndex(23) + length(8) exceeds writerIndex(24): PooledUnsafeDirectByteBuf(ridx: 23, widx: 24, cap: 24)
at io.netty.handler.codec.ByteToMessageDecoder.callDecode(ByteToMessageDecoder.java:442) ~[netty-all-4.1.9.Final.jar:4.1.9.Final]
at io.netty.handler.codec.ByteToMessageDecoder.channelInputClosed(ByteToMessageDecoder.java:375) ~[netty-all-4.1.9.Final.jar:4.1.9.Final]
at io.netty.handler.codec.ByteToMessageDecoder.channelInputClosed(ByteToMessageDecoder.java:342) ~[netty-all-4.1.9.Final.jar:4.1.9.Final]
at io.netty.handler.codec.ByteToMessageDecoder.channelInactive(ByteToMessageDecoder.java:325) ~[netty-all-4.1.9.Final.jar:4.1.9.Final]
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelInactive(AbstractChannelHandlerContext.java:245) [netty-all-4.1.9.Final.jar:4.1.9.Final]
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelInactive(AbstractChannelHandlerContext.java:231) [netty-all-4.1.9.Final.jar:4.1.9.Final]
at io.netty.channel.AbstractChannelHandlerContext.fireChannelInactive(AbstractChannelHandlerContext.java:224) [netty-all-4.1.9.Final.jar:4.1.9.Final]
at io.netty.handler.codec.ByteToMessageDecoder.channelInputClosed(ByteToMessageDecoder.java:360) [netty-all-4.1.9.Final.jar:4.1.9.Final]
at io.netty.handler.codec.ByteToMessageDecoder.channelInactive(ByteToMessageDecoder.java:325) [netty-all-4.1.9.Final.jar:4.1.9.Final]
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelInactive(AbstractChannelHandlerContext.java:245) [netty-all-4.1.9.Final.jar:4.1.9.Final]
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelInactive(AbstractChannelHandlerContext.java:231) [netty-all-4.1.9.Final.jar:4.1.9.Final]
at io.netty.channel.AbstractChannelHandlerContext.fireChannelInactive(AbstractChannelHandlerContext.java:224) [netty-all-4.1.9.Final.jar:4.1.9.Final]
at io.netty.handler.codec.ByteToMessageDecoder.channelInputClosed(ByteToMessageDecoder.java:360) [netty-all-4.1.9.Final.jar:4.1.9.Final]
at io.netty.handler.codec.ByteToMessageDecoder.channelInactive(ByteToMessageDecoder.java:325) [netty-all-4.1.9.Final.jar:4.1.9.Final]
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelInactive(AbstractChannelHandlerContext.java:245) [netty-all-4.1.9.Final.jar:4.1.9.Final]
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelInactive(AbstractChannelHandlerContext.java:231) [netty-all-4.1.9.Final.jar:4.1.9.Final]
at io.netty.channel.AbstractChannelHandlerContext.fireChannelInactive(AbstractChannelHandlerContext.java:224) [netty-all-4.1.9.Final.jar:4.1.9.Final]
at io.netty.channel.ChannelInboundHandlerAdapter.channelInactive(ChannelInboundHandlerAdapter.java:75) [netty-all-4.1.9.Final.jar:4.1.9.Final]
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelInactive(AbstractChannelHandlerContext.java:245) [netty-all-4.1.9.Final.jar:4.1.9.Final]
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelInactive(AbstractChannelHandlerContext.java:231) [netty-all-4.1.9.Final.jar:4.1.9.Final]
at io.netty.channel.AbstractChannelHandlerContext.fireChannelInactive(AbstractChannelHandlerContext.java:224) [netty-all-4.1.9.Final.jar:4.1.9.Final]
at io.netty.channel.ChannelInboundHandlerAdapter.channelInactive(ChannelInboundHandlerAdapter.java:75) [netty-all-4.1.9.Final.jar:4.1.9.Final]
at io.netty.handler.timeout.IdleStateHandler.channelInactive(IdleStateHandler.java:278) [netty-all-4.1.9.Final.jar:4.1.9.Final]
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelInactive(AbstractChannelHandlerContext.java:245) [netty-all-4.1.9.Final.jar:4.1.9.Final]
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelInactive(AbstractChannelHandlerContext.java:231) [netty-all-4.1.9.Final.jar:4.1.9.Final]
at io.netty.channel.AbstractChannelHandlerContext.fireChannelInactive(AbstractChannelHandlerContext.java:224) [netty-all-4.1.9.Final.jar:4.1.9.Final]
at io.netty.channel.DefaultChannelPipeline$HeadContext.channelInactive(DefaultChannelPipeline.java:1329) [netty-all-4.1.9.Final.jar:4.1.9.Final]
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelInactive(AbstractChannelHandlerContext.java:245) [netty-all-4.1.9.Final.jar:4.1.9.Final]
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelInactive(AbstractChannelHandlerContext.java:231) [netty-all-4.1.9.Final.jar:4.1.9.Final]
at io.netty.channel.DefaultChannelPipeline.fireChannelInactive(DefaultChannelPipeline.java:908) [netty-all-4.1.9.Final.jar:4.1.9.Final]
at io.netty.channel.AbstractChannel$AbstractUnsafe$7.run(AbstractChannel.java:744) [netty-all-4.1.9.Final.jar:4.1.9.Final]
at io.netty.util.concurrent.AbstractEventExecutor.safeExecute(AbstractEventExecutor.java:163) [netty-all-4.1.9.Final.jar:4.1.9.Final]
at io.netty.util.concurrent.SingleThreadEventExecutor.runAllTasks(SingleThreadEventExecutor.java:403) [netty-all-4.1.9.Final.jar:4.1.9.Final]
at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:442) [netty-all-4.1.9.Final.jar:4.1.9.Final]
at io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:858) [netty-all-4.1.9.Final.jar:4.1.9.Final]
at java.lang.Thread.run(Unknown Source) [?:1.8.0_221]
Caused by: java.lang.IndexOutOfBoundsException: readerIndex(23) + length(8) exceeds writerIndex(24): PooledUnsafeDirectByteBuf(ridx: 23, widx: 24, cap: 24)
at io.netty.buffer.AbstractByteBuf.checkReadableBytes0(AbstractByteBuf.java:1396) ~[netty-all-4.1.9.Final.jar:4.1.9.Final]
at io.netty.buffer.AbstractByteBuf.readLong(AbstractByteBuf.java:792) ~[netty-all-4.1.9.Final.jar:4.1.9.Final]
at io.netty.buffer.AbstractByteBuf.readDouble(AbstractByteBuf.java:818) ~[netty-all-4.1.9.Final.jar:4.1.9.Final]
at net.minecraft.network.PacketBuffer.readDouble(PacketBuffer.java:954) ~[gy.class:?]
at net.minecraft.network.play.server.SPacketSpawnObject.func_148837_a(SourceFile:93) ~[hx.class:?]
at net.minecraft.network.NettyPacketDecoder.decode(SourceFile:40) ~[gz.class:?]
at io.netty.handler.codec.ByteToMessageDecoder.callDecode(ByteToMessageDecoder.java:411) ~[netty-all-4.1.9.Final.jar:4.1.9.Final]
... 35 more

More info: I also found that it kicks you when looking at a blaze-like mob from this mod

This is the client log when players log in to the server, it's the same whether it's sinlgeplayer or multiplayer, it's just that singleplayer doesn't crash while in MP the player gets kicked.

That section you pasted is only in the singlepayer log, and it doesn't seem to have anything to do with wizardry. Since the server kept running but the players disconnected, this must be a client crash, so to find the cause I need the log/crash report from one of the players when connected to the server.

On closer inspection, it's actually the part above the bit you posted above which is relevant:

Caused by: java.lang.ArrayIndexOutOfBoundsException: 10
	at net.minecraft.network.PacketBuffer.func_179257_a(PacketBuffer.java:186) ~[gy.class:?]
	at net.minecraft.network.play.server.SPacketSoundEffect.func_148837_a(SourceFile:40) ~[kq.class:?]

It's actually the same crash as #198.