Hi Clementine,
I have reported the epic energy bug multiple times, and I have reported it in detail, but here is how it happens for me:
I start fighting on Skeletons Tomb (normal) until the Epic Boss Appears
I pick my knights to battle the Boss
I click next etc until I get to the Epic Boss and my Knights
I click Fight! and get the lovely wheel (Wheel of Doom) the elements spinning around.
After a period of time I get an error message (must take a picture of the exact message) which says server error
I click Retry, after some time the message appears again, and again
Finally I am kicked back out into the game, and my epic energy has gone.
Hope that helps.