All combat is "combo mode"

On my server combat often looks like a "combo mode", meaning there is no hit delay (i am using 1.8 combat mechanics). All plugins are stock except one, but it doesn't do anything that weird outside of canceling some hit events, which I dont think would cause this weird behaviour.

Any advice on how I could fix this?

Edit:
Example of what I mean by "combo mode":


As you can see, there is no attack cooldown whatsoever, so a hit can be registered every single tick.

update: it seems that relogging has some effect, and some players have no delay while others dont. my friend had no delay while I had normal delay. I then relogged and it was fine.

EDIT by Moderator: merged posts, please use the edit button instead of double posting.

 

We can't help you without seeing your code.

 

There isn't really any. It still happens even when I am not running any plugins whatsoever.

 

Update:

The damage is also increased in lava. In lava, people take damage every tick.

 

It's pretty likely that the plugin you mentioned is the culprit as you also said it's tampering with hit events. Shouldn't hurt to try to investigate it too?
Or it could be another different thing, such as accelerated server TPS. A big but, is that I have only heard of this and never seen it being truly mentioned as an issue or experienced it myself.

A bandage could be that you listen for the EntityDamageByEntityEvent, schedule a Task that runs 1 tick later (synchronously of course) and forcefully & manually sets the player's no damage ticks to its max no damage ticks (which is 20).