java.lang.NoClassDefFoundError: Could not initialize class com.comphenix.protocol.PacketType$Play$Client
at com.comphenix.protocol.PacketType.getLookup(PacketType.java:602)
at com.comphenix.protocol.PacketType.fromCurrent(PacketType.java:786)
at com.comphenix.protocol.injector.netty.NettyProtocolRegistry.associatePackets(NettyProtocolRegistry.java:207)
at com.comphenix.protocol.injector.netty.NettyProtocolRegistry.initializeNew(NettyProtocolRegistry.java:184)
at com.comphenix.protocol.injector.netty.NettyProtocolRegistry.initialize(NettyProtocolRegistry.java:49)
at com.comphenix.protocol.injector.netty.ProtocolRegistry.(ProtocolRegistry.java:59)
at com.comphenix.protocol.injector.netty.NettyProtocolRegistry.(NettyProtocolRegistry.java:43)
at com.comphenix.protocol.injector.packet.PacketRegistry.initialize(PacketRegistry.java:54)
at com.comphenix.protocol.injector.packet.PacketRegistry.getClientPacketTypes(PacketRegistry.java:112)
at com.comphenix.protocol.injector.PacketFilterManager.(PacketFilterManager.java:211)
at com.comphenix.protocol.injector.PacketFilterBuilder.buildInternal(PacketFilterBuilder.java:185)
at com.comphenix.protocol.injector.PacketFilterBuilder.build(PacketFilterBuilder.java:177)
at com.comphenix.protocol.ProtocolLib.onLoad(ProtocolLib.java:198)
at org.bukkit.craftbukkit.v1_16_R3.CraftServer.loadPlugins(CraftServer.java:394)
at net.minecraft.server.v1_16_R3.DedicatedServer.init(DedicatedServer.java:263)
at net.minecraft.server.v1_16_R3.MinecraftServer.w(MinecraftServer.java:1061)
at net.minecraft.server.v1_16_R3.MinecraftServer.lambda$a$0(MinecraftServer.java:291)
at java.base/java.lang.Thread.run(Thread.java:834)
Dump:
Parameters:
[NULL]
Sender:
com.comphenix.protocol.ProtocolLib@1f79a551[
statistics=
backgroundCompiler=
packetTask=-1
tickCounter=0
unhookTask=com.comphenix.protocol.injector.DelayedSingleTask@2964c925
configExpectedMod=-1
updater=com.comphenix.protocol.updater.SpigotUpdater@6006a29b
redirectHandler=
commandProtocol=
commandPacket=
commandFilter=
packetLogging=
skipDisable=false
isEnabled=false
loader=org.bukkit.plugin.java.JavaPluginLoader@59e19645
server=CraftServer{serverName=Purpur,serverVersion=git-Purpur-1053,minecraftVersion=1.16.5}
file=plugins/ProtocolLib.jar
description=org.bukkit.plugin.PluginDescriptionFile@4c23ead
dataFolder=plugins/ProtocolLib
classLoader=PluginClassLoader{plugin=ProtocolLib v4.6.0-SNAPSHOT-b483, pluginEnabled=false, url=plugins/ProtocolLib.jar}
naggable=true
newConfig=YamlConfiguration[path='', root='YamlConfiguration']
configFile=plugins/ProtocolLib/config.yml
logger=com.destroystokyo.paper.utils.PaperPluginLogger@483a10f
]
Version:
ProtocolLib v4.6.0-SNAPSHOT-b483
Java Version:
11.0.10
Server:
git-Purpur-1053 (MC: 1.16.5)

Forgot to update to latest version of ProtocolLib