I had seen a few threads long ago on the subject, but NONE had received any form of acknowledgement, and all are archived / unable to be found ( even the ones I've posted in ).
This bug has been present ever since the update that changed how enemies perceive and react to noises/damage from a player in stealth ( U19.6.3, almost 2 years ago ). Any ranged weapon kill that includes damage from extra projectiles via multishot will NOT count as a stealth kill. It will only count if it only takes one of the shots to deal enough damage to kill the enemy. Yes, this has been thoroughly tested by multiple players. Yes, the enemies had been spawned for FAR longer than the allotted 5 seconds. Yes, the enemies were not alerted. It is far too easily reproducible, and I know a lot of you have most likely noticed some sudden drops on your stealth kills for no clear reason at least a few times.
I do hope that this particular issue is finally addressed, it's important to at least some people that enjoy doing stealth, I'd think.