By 'icon will not show a cool down' do you mean your Provoke is still available - as if you didn't use it? I'm guessing you're just experiencing latency/lag during 0.5's entry animation or during Voke use.

Animations and vfx are player-side, not server, so you could see yourself actually do the ability even during a lag spike, but once the spike ends and you catch back up with the server, the CD never actually registered. For a moment like using Provoke it'd be very noticeable.

Most noticeable for me is when I experience this (occasionally) as DRG with Jump oGCDs. Lag spike whist weaving a Jump, resulting in a double-Jump that cost me some GCD delay. When it happens though I just like to think I'm lucky it wasn't a full 90k d/c.