Unseen Form works with Black Knife Armor and Crepus' Vial (fix)

Elden Ring categorizes and prioritizes which visual effects can be applied at one time. Unfortunately, silent foot steps is considered a visual effect which for some reason overwrites visual camouflage effects. (ie you don't appear transparent after casting Unseen Form if you are wearing Black Knife armor or the Crepus' Vial talisman). You're getting both buffs, it's just a cosmetic bug. Changing the priority of the silence visual allows both effects to be applied simultaneously.

With Yapped, in SpEffectVfxParam change

6018010 Play Priority from 0 to 12 (Black Knife silence visual effect)

360000 Play Priority from 0 to 12 (Crepus' Vial silence visual effect)

or download and import the attached csv (modified from 1. 04)

I'm not going to update the csv for future updates, the instructions are here. Will these priorities override other visual effects? Who knows, there are hundreds of them! Play with the values until an official fix if you need, at least you know where to look now :D