Hi there everyone... Tks for the replies !
I'm genttle with the speedbrake lever, there's even a video on Airbus Win discussing this topic (hammering it).
I had the chance to fly the 321neo during the last days and took closer look awaiting the described situation to happen again. It didn't ! I even tested disarming the lever while at Idle Rev and, as I commented before, none of the spoilers retracted.
Anyway, I don't know what could happened, probably some glitch god knows where down the path between the lever and the actual surface...