Everytime a player disconnect on my server, i get lagspike for 5 sec. gets a server overloaded message then it runs normally.

Removed all plugin and added one after one and found out its this plugin.

Tried to run only this plugin and same result. when Vault is installed then it lag everytime someone logs off.

Some server specc

Server specc:
OP: Windows Server 2008
Motherboard: MSI 970A.G46 SLI
CPU: AMD FX-4100 X4 4.0GHz (Bulldozer)
RAM: G.Skill 16GB CL11 2133Mhz
HDD: A-Data SSD Premier Pro SP900 128GB /(6gb/sec)
Connection: 100/100 Fiber

Well as i said in the post above, it make that lag even when i have no other plugins active.but gonna try on a new fresh server too to be sure, ill be back with result

No you didn't. You said you added one after another (implying not removing previous plugins). In addition, Vault has no active portions, if no plugins use it, it does nothing. If your server is lagging when a player joins it has absolutely nothing to do with Vault.

This is not a Vault issue. you have another plugin that is using vault for some other operations that are enabled when Vault is on the server. Simply adding plugins one by one will not work if the other plugin is on the server and then you add in Vault, obviously it will lag since the other plugin now sees Vault and does it's extra stuff.