It's possible that you're trying to "queue" to many actions at once, one of them being the health potion. As long as you're doing it within your turn and don't try to click too many actions at once (let's say glyph of descruction/potion/elixir of endurance and other actions) within single turn quickly you should be just fine.

Ihit - I too have had this issue where I've clicked something but nothing happened (only one thing in a turn e.g a life potion), I thought to begin with I was just not clicking it properly, but after the 50th time of it and then reading this maybe I'm not going crazy after all ;)

its happen to me a few times to. usualy in AOH or 7 bridges and usualy when im low on health

It could very well be that I am "queueing" too many actions at once, but that's not always the case. Sometimes I will attack someone or something and that is low enough on health that my attack could result in a kill. In order to save on potions, I will wait until I attack before healing. If I get the kill, most of the time the potion is not consumed. If I don't get the kill, it usually is consumed before I am attacked. (although, I have gotten a kill shot, then consumed a potion AFTER the opponent died). I have used this method often while doing eyes.
Again, I will hear the audible click indicating that the potion was selected, even though it may not be consumed. I will just continue to adapt my play style to anticipate this as normal.
Thank you for the reply.