thanks, i'm going to test and give you feedback
So, those are the problems I found:
1: Can only trigger a double attack if proc a crit first. as shown by the video below, if you have low / no critical rate, you won't activate a double attack. the expected behavior is that crit rate doesn't influence the chance of trigger a double attack, but whenever activating a DA, it should be a critical hit.
2: Being able to proc double attack with katar without sidewinder, it shouldn't be possible. Also when equipping a Sidewinder card, the double attack rate seems much lower than it should, probably because it reads as a level 1 skill.