just played a match and near the end, for my second turn wanted to activate the lvl 10 heat shield. however the button was not responding, so I cooled down instead. I also had no energy at the time. but surely I should have been able to activate a heat shield??

Maybe the server went crazy and thought it was a energy shield. I had something weird happen with a double blue watch guard that took the place of a sword. I only own one, but in a few battles, I had two, one was where my sword was supposed to be.

True.. I think so.
That's why when it happened to me, I reported it to the admins... it's either they probably have forgotten about that or it's not a bug. If it's the first one, I'm glad that you have created a thread about this, something that can remind them about this. If it's the second one, there is nothing to be done.