I obviously did my tests without buff who needs mana to sustain (so not Mage Armor) and even with somes, the same problem persists.
It is not that I dont get all my mana regen per second but that it is not effective every seconds.

Hi there,
I just realized my mana regeneration is not always ticking.
I tested it in town doing nothing after emptying my mana pool and sometimes I didn't regain my mana each second.
It is completely random, in a minute and a half it happened 5 times, at differents intervals (19, 27, 20 and 17 seconds).