I don't know why Flurry does not crit every hit in your tests. I tested it with dual daggers and backstab and it crits every time
Just a quick aside, backstabs are by nature always critical attacks. I'm not sure if you mis-typed or not here.
The third hit of flurry not causing a critical hit is strange, it's possible it's just not programmed as a normal physical attack, or its damage is rolled into the three attacks and only two critical hits show visually. Someone who can look at the code on pc could answer this, I'm just a console player.
I suspect it's an oversight because onslaught and daggers drawn both can crit on every hit. (I've seen daggers drawn crit while attacking from the front)
