I don't think there was a nerf. I think it's likely just remodded. There was a similar post to this the other day. I tested it and my vader still couldn't land debuffs when geared with a speed set and a potency set even after people were complaining about the nerf. I did arena battles against several teams and still couldn't land debuffs on opening aoe.
Then I remodded putting a potency cross and two potency sets on vader and increasing potency secondaries where it didn't cost too much speed. Brought his potency up to about 80%. Now debuffs land at least some of the time.
I don't think they changed anything. Likely just people figuing ou how to mod to counter it. It will likely become more prevalent when the mod sets finally change.
You may have to actually mod for tenacity to keep teams modded for potency from debuffing your bastilla team.