There are no planned events that reduce your active or map mana in the game. To troubleshoot this,I'll need details on what happened before you noticed the change. Also, try sleeping. Maybe it's not max mana, but just your current mana pool that is 0.
Oh, and if you used any kind of save editor - that's on you.
I was doing the mermaid quest I was at like the last quest where I defeat the fire phoenix after that I slept went to hunt on feline hunting grounds for the second time I was fighting a mongirl and that was when I noticed my mp became 0/0 when I tried to use a mp Regen item, when I was fighting the phoenix it wasn't 0/0 it was like 14/14 I don't know what happened
