Verso Perfection sometimes stuck on "D"

[RealKarl]

At least a couple of fights, I was unable to inrcrease Verso's Perfection. It was stuck on "D". Free shots, auto attacks, no change in Perfection. It's probably some intended game mechanic, but I couldn't figure out why. Maybe Powerless debuff? Any ideas?

[2seks]

Check his weapon traits.

[......]

if u use blodam [weapon] if u full life u rank never go up if u lower the hp higher rank u get

[Yfann]

I have the same issue, and none my weapon nor any luminas should disable that :(
Thought it was invert at first but even if Verso doesn't have any buff/debuff sometime it doesn't work