I’ve already reported this two months ago. Graphical Glitches (Residual Artifacts) from Projectiles
It’s been around for at least two seasons, if not three. At one point it seems they did fix it for a brief while after my report, or at least tried to, and the duration of the linger shortened significantly, but I noticed it’s back again this season. I couldn’t post a reply directly to my own original thread without someone else replying before me, so I just edited it with an update, but not sure if they actually see that. At the time I saw, it looked like the bug was manifested for Symmetra right clicks, but now I’ve seen it show up for Genji and Lucio’s projectiles again too. So the bug is back full force.
Please make a reply in my linked thread as the information there describes the bug in full, including the specific conditions for replication. It doesn’t actually happen in every normal match.