Error stacktrace:
[21:49:57 INFO]: Error Unable to inject incoming channel [id: 0x8319eda8, L:/XXX:25565 - R:/XXX:63562]. (java.lang.IllegalArgumentException: Unable to find NetworkManager in [id: 0x8319eda8, L:/XXX:25565 - R:/XXX:63562]) occured in com.comphenix.protocol.injector.netty.ProtocolInjector@25744cb.
[21:49:57 ERROR]: [ProtocolLib] INTERNAL ERROR: Unable to inject incoming channel [id: 0x8319eda8, L:/XXX:25565 - R:/XXX:63562].
If this problem hasn't already been reported, please open a ticket
at https://github.com/dmulloy2/ProtocolLib/issues with the following data:
Stack Trace:
java.lang.IllegalArgumentException: Unable to find NetworkManager in [id: 0x8319eda8, L:/XX:25565 - R:/XXX:63562]
at com.comphenix.protocol.injector.netty.InjectionFactory.findNetworkManager(InjectionFactory.java:209)
at com.comphenix.protocol.injector.netty.InjectionFactory.fromChannel(InjectionFactory.java:142)
at com.comphenix.protocol.injector.netty.ProtocolInjector$1.initChannel(ProtocolInjector.java:157)
at io.netty.channel.ChannelInitializer.initChannel(ChannelInitializer.java:129)
at io.netty.channel.ChannelInitializer.handlerAdded(ChannelInitializer.java:112)
at io.netty.channel.AbstractChannelHandlerContext.callHandlerAdded(AbstractChannelHandlerContext.java:938)
at io.netty.channel.DefaultChannelPipeline.callHandlerAdded0(DefaultChannelPipeline.java:609)
at io.netty.channel.DefaultChannelPipeline.addLast(DefaultChannelPipeline.java:223)
at io.netty.channel.DefaultChannelPipeline.addLast(DefaultChannelPipeline.java:381)
at io.netty.channel.DefaultChannelPipeline.addLast(DefaultChannelPipeline.java:370)
at com.comphenix.protocol.injector.netty.ProtocolInjector$2.initChannel(ProtocolInjector.java:171)
at io.netty.channel.ChannelInitializer.initChannel(ChannelInitializer.java:129)
at io.netty.channel.ChannelInitializer.handlerAdded(ChannelInitializer.java:112)
at io.netty.channel.AbstractChannelHandlerContext.callHandlerAdded(AbstractChannelHandlerContext.java:938)
at io.netty.channel.DefaultChannelPipeline.callHandlerAdded0(DefaultChannelPipeline.java:609)
at io.netty.channel.DefaultChannelPipeline.access$100(DefaultChannelPipeline.java:46)
at io.netty.channel.DefaultChannelPipeline$PendingHandlerAddedTask.execute(DefaultChannelPipeline.java:1463)
at io.netty.channel.DefaultChannelPipeline.callHandlerAddedForAllHandlers(DefaultChannelPipeline.java:1115)
at io.netty.channel.DefaultChannelPipeline.invokeHandlerAddedIfNeeded(DefaultChannelPipeline.java:650)
at io.netty.channel.AbstractChannel$AbstractUnsafe.register0(AbstractChannel.java:502)
at io.netty.channel.AbstractChannel$AbstractUnsafe.access$200(AbstractChannel.java:417)
at io.netty.channel.AbstractChannel$AbstractUnsafe$1.run(AbstractChannel.java:474)
at io.netty.util.concurrent.AbstractEventExecutor.safeExecute(AbstractEventExecutor.java:164)
at io.netty.util.concurrent.SingleThreadEventExecutor.runAllTasks(SingleThreadEventExecutor.java:472)
at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:500)
at io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:989)
at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74)
at java.base/java.lang.Thread.run(Thread.java:834)
Dump:
manager:
com.comphenix.protocol.injector.PacketFilterManager@20a464e9[
unhookTask=com.comphenix.protocol.injector.DelayedSingleTask@77195f1
packetListeners=[]
packetInjector=com.comphenix.protocol.injector.netty.ProtocolInjector$5@40c5c074
playerInjection=com.comphenix.protocol.injector.netty.ProtocolInjector$4@7ac7ac07
interceptWritePacket=com.comphenix.protocol.injector.packet.InterceptWritePacket@79c70c9a
inputBufferedPackets=[]
recievedListeners=com.comphenix.protocol.injector.SortedPacketListenerList@7212d04e
sendingListeners=com.comphenix.protocol.injector.SortedPacketListenerList@1c3a6818
hasClosed=false
classLoader=org.bukkit.plugin.java.PluginClassLoader@3892c5df
reporter=com.comphenix.protocol.ProtocolLib$1@1ab82c31
server=CraftServer{serverName=CraftBukkit,serverVersion=VSpigot,minecraftVersion=1.8.8}
library=ProtocolLib v4.5.1
asyncFilterManager=com.comphenix.protocol.async.AsyncFilterManager@31f9c2f1
knowsServerPackets=true
knowsClientPackets=true
phaseLoginCount=0
phasePlayingCount=0
packetCreation=false
spigotInjector=
nettyInjector=com.comphenix.protocol.injector.netty.ProtocolInjector@25744cb
pluginVerifier=com.comphenix.protocol.injector.PluginVerifier@6de53f4d
hasRecycleDistance=true
minecraftVersion=(MC: 1.8.8)
loginPackets=com.comphenix.protocol.injector.LoginPackets@4ac9250f
debug=false
]
Sender:
com.comphenix.protocol.injector.netty.ProtocolInjector@25744cb[
injected=true
closed=false
playerFactory=com.comphenix.protocol.injector.server.TemporaryPlayerFactory@38f25661
bootstrapFields=[VolatileField [accessor=com.comphenix.protocol.reflect.accessors.Accessors$SynchronizedFieldAccessor@267460d9, container=net.minecraft.server.v1_8_R3.ServerConnection@c1f7b28, previous=[AbstractBootstrap$PendingRegistrationPromise@3849b9ef(success)], current=com.comphenix.protocol.injector.netty.BootstrapList@1af58afe, previousLoaded=true, currentSet=true, forceAccess=false], VolatileField [accessor=com.comphenix.protocol.reflect.accessors.Accessors$SynchronizedFieldAccessor@1f0243d1, container=net.minecraft.server.v1_8_R3.ServerConnection@c1f7b28, previous=[], current=null, previousLoaded=true, currentSet=false, forceAccess=false]]
injectionFactory=com.comphenix.protocol.injector.netty.InjectionFactory@6833bd22
networkManagers=[]
sendingFilters=com.comphenix.protocol.concurrency.PacketTypeSet@1d40e70a
reveivedFilters=com.comphenix.protocol.concurrency.PacketTypeSet@2bd43c26
mainThreadFilters=com.comphenix.protocol.concurrency.PacketTypeSet@26c5ee46
bufferedPackets=com.comphenix.protocol.concurrency.PacketTypeSet@536a9d11
invoker=com.comphenix.protocol.injector.PacketFilterManager@20a464e9
reporter=com.comphenix.protocol.ProtocolLib$1@1ab82c31
debug=false
]
Version:
ProtocolLib v4.5.1
Java Version:
11.0.9
Server:
VSpigot (MC: 1.8.8)

My NetworkManager.class
https://hastebin.com/qakidafebi.kotlin

Try the latest dev build. We fixed an issue with newer Java versions recently

this issue seems to experience the same issue as above #1002
I tried to upgrade the netty networking from paper 1.8.8 base version(4.0.23.Final) to 4.1.56.Final logging in to the server works fine I can do everything
but I get the same error on the same lines as above
my testing was done with ProtocolLib v4.6.0-SNAPSHOT-b1
in both java 8 and java 11

I don't know if the issuer did the same to his spigot or the one on the referenced issue

maybe this is some helpful information

The error is present in Netty 4.1.50.Final, is a issue from ProtocolLib end i think

aadnk/ProtocolLib@2e21333

This pull request fix's the issue, im not getting the spam in console with that patch