Ty for informations.
The case is, when they introduced this unlocable Healthbar, you were able to move around Monster's information bar (the one that can be moved), but regular health bar (without any additional informations) would still be displayed above monster's head.
I find this very useful, as I don't want extra informations to narrow my visible sight while killing stuff around, but I still like to see how much HP they got left (the unmovable health bar without any other additional informations).
It used to be like this from start, but then HP bars started glitching and mine completely dissapeared.
Hopefully they'll fix this!