Vel'Koz, Warwick, and Skarner Ultimate bugs

While i do not have evidence, I have encountered bugs where these three champion's Ultimate abilities activate but do nothing. To clarify, for Warwick and Skarner the enemy does not become stunned/silenced when I use it. I have only encountered these once or twice within recent months, however I do encounter a Vel'Koz bug where he will do the animation for the ult and i will be rooted, but the beam does not appear and I do no damage BUT Organic Deconstruction stacks, quite regularly. I play all three of these champions quite often, and if I do encounter the problem again I will try my best to post evidence here.