My mana in war gets to maxed and then goes away before I can hit them. Not fighting anyone that takes my mana away. Today isn’t the first time. Again only fighting joon, Elena, Freya, jean, ratatoskr
Not sure which heros you are battling, as there are a number that can steal mana which might explain the vanishing mana.
Screen shots or videos would help to illustrate the issue you are having.
Freya is part of the vanaheim realm. When she dies she takes 5% mana away from all heroes. If there are more family members on their team then more mana is taken when they die. That might be it.