Description
Here you send a PacketContainer instead of the underlying packet (event.addPacketAfter(packet.deepClone()) instead of event.addPacketAfter(packet.deepClone().handle)).
This causes problem with our plugin, OldCombatMechanics.
Related issues
kernitus/BukkitOldCombatMechanics#355
ProtocolSupport/ProtocolSupport#1187
Mitigation
I have not looked at your code in-depth enough to tell if the above is correct, but it solves the problem and if I understand what addPacketAfter does correctly, it should be correct.
I will also add a mitigation in OCM that just ignores other classes (maybe silently) to stop OCM from crashing, but the proper fix should be done here, IMHO.