I think this is an old complaint but since I was noticing this again recently, here it is: Spamming skills seems to result, quite often, in one or more going into cool-down but not firing. For example, lightning, icestorm, then firestorm. Usually ice fires, but I might get one or none of the other two. It's particularly noticeable for firestorm since I'm firing it to throw the mass of mobs away and nothing happens to any of them. Not even any damage.

And of course, I then have to try to run and/or spam pots until I can use the skills again.

Reminder to self: wait a tick. wait a tick. wait a tick. Especially when lagging: wait a tick.