Whenever someone throws a Dreadium Katana Sword from AbyssalCraft (edit: also happens with other items etc. from other mods and Vanilla Items (like vanilla seeds to name an example)) to the ground, he gets kicked from the Server with the following message:
https://pastebin.com/T9X7Yk6J

It should be noted that the log indicates that the problem is caused by the following line
in TechReborn:

Minecraft 1.11.2
Forge Mod Loader version 13.20.1.2454
TechReborn-1.11.2-2.3.3.181
AbyssalCraft Integration-1.11.2-1.5.0
AbyssalCraft-1.11.2-1.9.4-pre-4

Not reproduced