Am I doing concealment wrong?

It seems like half the time I try to use this skill, I either don’t enter stealth at all, or am in it for maybe a fraction of a second before it breaks.

The skill says it doesn’t break upon taking damage… so what is it?

My only guess is that some sort of lingering effect or projectile from a previous attack (I’m using heartseeker + rapid fire) is causing the game to think I “performed” an attack during stealth and breaking it.

Can anyone confirm?

You’re likely attacking with your movement. Having attack on the same movement tends to cause this.