Tahm Kench Q in URF
This is not exactly a bug, but is what I think is essentially an oversight.
In URF, Tahm's Q CD is capped at 2.4 seconds, when from the cooldown in normal games (around 4 or 5 seconds at max rank), it should go down to 1 or 0.8 seconds.
I know this was probably put in place in the past in URF for Tahm because his Q used to stack his passive and used to not consume the passive mark on stun, which would mean that he would have been able to permastun people.
But, now that he has been changed since then, his Q can no longer permastun or even stack his passive, so I think the URF-specific nerf of making his Q have a 2.4 second cooldown can likely be removed, and was probably left on unintentionally since previous URF iterations.