This sounds like what I was experiencing. I didn’t realize until this post Tassadar Shadow Walk Talent Cancelleable pointed it out that you can cancel the talent early by hitting the key again. I went into try mode and found that to be the case for me. I thought that damage was revealing me because in-game it can be kind of an “Oh s***!” button to get out when you’re taking too much damage, and those are situations where you’re likely to spam the key a few times without realizing it.
But it shouldn’t be cancellable, right? Wouldn’t that defeat the purpose?