https://answers.ea.com/t5/Bug-Reports/Stunning-Tactics-not-tracking-Stuns-properly/m-p/12413226
As I have said, I have been in this position before. Also I just used SLKR, KRU, Thrawn, Palpatine and Count Dooku to complete the feat in this current challenge. Perhaps, if you are using normal Kylo Ren, You are counting uses of Sp2 as a stun when he is not at full health. And if you do use Dooku, Not all of his basics will inflict stun either.
I logged this issue to find a solution to the issue, not asking for "what else can I use ?"
I don't use OG Kylo - not relevant. I use SLKR and KRU for 12 minutes straight (after EP and 2 more die) to constantly apply stun, and it doesn't count somehow.
The question is why SLKR's stuns are not accepted properly.
