Problem/Bug Players not taking knockback in my server[Glitch]

Okay, so I have this glitch/bug that my players do not take any knockback at all in my server. Idk what it is that makes this happen but it only seems like players who play from the same ip as me (same home) take knockback, and yes, this is a home-hosted server. I really hope someone can help me fix this glitch

Lastly here is a list of my pluginsmaybe one of them is making this glitch happen?)

Worldedit, Essentials, PermissionsEX, Worldguard, CScorelib, BkCommonLib, WarpSigns, Mycommand, Kits, PrisonUtils, PrisonMineplugin, Hubby, ServerSigns, JustWarp, Myworlds(Like Mulitverseworlds), ZavAutomessenger.

Also I am running spigot 1.8.5 jar.

Thanks.

-Zactybioz

Here is a video demonstration of the glitch:

 

I suggest whitelisting your server so that while you're testing the following only you and a friend can go on.

1. Backup server just in case. (Make a zipped copy or something)
EDIT: 1.5. Remove all plugins to ensure that it's a plugin problem. If not, update Spigot.
2. Remove half of plugins. Removed half is A group and half on the server is B group.
3. If problem doesn't exist anymore, then problem that causes problem is in A, else B.
4. If problem still exists, then problem is in group B, not A.

5. If group A is the problem:
Add half of A group back, if problem exists then remove half of the plugins that you put back on. and go back to step 3/4.

6. If group B is the problem:
Remove another half of plugins. If problem persists, remove another half etc. If it's in the removed group then add half back.


Hope I explained that okay.