It is blocking dht for sure. You could still be sensitive to the remaining 50% of scalp dht that is left on your scalp. Or you could be extra sensitive to the spike of scalp T/serum. T is also an androgen afterall. Or your hormone levels arent good enough due to dutasteride. In my case I think it was...
Ye dutasteride fucked my hair after 1.5 years of use. Lost like 10 hairs per day it was crazy. Semen just seeped out slowly and ended up ejaculating 1 drop of semen..it castrated me but my hair got twice as thin. Hormones man.