If the knockback enchantment is too high, in this preticular example at lvl. 32767, it wil make lag, as shown in the video.

How to reproduce it:
1. Open chat, and type in/paste this command: 

/give @p minecraft:stick{Enchantments:[{id:"minecraft:knockback",lvl:32767}],display:{Name:"{\"text\":\"Lag Bug Stick\"}"}} 1

2. Find mob and punch it with the stick you have gived yourself
3. Voala, there is lag

Click here for video. (It have 33 MB, so this is why it is on YT)