So tonight a friend and i decided to hop on Halo MCC on PC to unlock the “Workers Compensation” achievement where you get a splatter kill on an enemy in Halo Reach. My friend was able to unlock both the achievement and banner with no problems, but for some reason even though i have definitely gotten the medal and the kill some 10+ times, Neither the steam achievement or the banner have unlocked for me. I tried all sorts of ways to get the kill, and tried all sorts of other troubleshooting tips i’ve found, but to no avail. I know it’s not the problem where no achievements are available to unlock cause i have unlocked around 7 others. Has anyone else experienced this? If so, how did you fix it? 
Hello there ThePRIMEevil 0,
In order to get the achievement, you have to splatter an enemy with the forklift. So not just any splatter with any vehicle.
What worked the easiest for me:
Game Mode: Firefight
Game Type: Gruntpocalypse
Map: Courtyard
Settings: Give yourself the Gravifty Hammer, make yourself invincible and make it so there is no time limit.
When you start the game run over to the Forklift and use your gravity hammer to smash it towards the grunts. Eventually it will land on or completely splatter a grunt and you will get the achievement and Nameplate.
Happy Gaming!
-Rare
Hi Rare! I realized when i read your reply that i left a vital piece of info out of my original post! 
I actually did do it with the forklift, i just forgot to write it, sorry! I actually did exactly what you said, using the grav hammer on gruntpocalypse in courtyard with the invincibility and no time limit, both in a game with my friend and without. We also tried doing firefight vs with no shields running each other over in the forklift, and we got the medal there too, but the achievement and nameplate still didn’t unlock. Sorry for the confusion!
Hi, we had the exact same problem with my brother getting it but me not. The problem was fixed when I hosted the firefight!
I had to switch over and host the game to get mine.
Same problem in the same exact tries. I can be by myself and not get it. Any known fix? Does 343 know?