This bug was there even in december when I first played. It is not about the effect not showing.
Cooldown is started, the thing supposedly fires, but neither the visual, nor damage happens.
It randomly stops working and once it stops it cant fire again, until you level the skill up. (temporary fix) And even that sometimes does not work.
If memory serves right, given enough time, it would always stop working.
That means, I never bothered to level up the beam again because it wasnt random once upon a time occurence, but always.
Start the game, use the kol beam right from the start and you are bound to experience the bug if you watch your unit. I was actually sure that you would have known about the issue, because it is so glaring and extremely easy to encounter. Consistently.