Oh okay, cool to know this is fixed now. I was filing complints like it was going out of fashion when I thought it was the intentional work of hackers, but then I was told it was Rockstar's F up.
Invisibles dudes always seemed to be low, single-digit level players toting the shotgun. They'd usually go something like 20-1, with the one death probably being a lucky grenade.
I know I could seem them on the minimap so I just started spraying in the general direction but you couldn't even lock onto their nothingness (no surprise really).
All said and done it was funny how despite having all the odds in their favour they'd never be the best player in the match.