rotary encoder strange behavior (too many datas)

That is strange... Do the pins need pullups?

Maybe swap A5 and A8 in the code and see if that helps. Also maybe you needed edge:'falling' in the watch.

Usually in an encoder, when one pin changes state, the state of the other pin determines the angle. But in this case I guess because we were reacting on both edges of A5, we'd just end up adding and subtracting from value