Bug or Cheat in 39 BGs???

If I am not on my main, I am usually playing 39 bracket pvp.

a few months ago in a battleground we came up against a Warlock who for some reason we could not attack. If he was targeted and we tried to cast a spell or attack on him we would get the message "spell not ready yet" despite the spells and attacks not being on cooldown and experiencing no status effects like silence, ect.

For some reason whenever he would tick drain life on one of us it, would trigger our global cooldown, so not only could we not attack this guy, but if he was attacking you, there was no blink, bubble, interupt, ect to get out of it.

We all suspected it was cheating. We stopped playing for a few days and he went away, but today I am having the same issue. If i try to attack a specific player (warlock again, different guy) i just get a message saying "spell not ready yet"

The first time it happened there were 3 of us in one room so we could see eachother's screens and knew we were seeing the same thing. Now I am alone so I dont know...

Can anyone help me figure out if this is a bug or if I am genuinely dealing with some sort of scripter, and how would I be able to prove it?

Edit: Issue has only ever happened while playing on horde side. Have never experienced the issue playing Ally.