Originally Posted by IrrRelevant
While playing with Panda Annie the bar suddenly reappeared... i just need to find out why
Got it: Just switch Colorblind mode, it will somehow reset the HUD and you'll see your mana bar. (it will still be visible after you switched it back)
Testing right now if it works for all Video settings
Edit2: Looks like you just need to change any Video setting to make it visible again (only works for the current game, next game its not visible again)
that would explain the volibear one i found, i had just changed my window to borderless to get a screenshot.
for those who will read this ^ this guys post explains the work around and why some people had them and others didn't.