Hi I am doing mission “Clear that jump gate” given by Jack Kiger in Wildfire Colony (Servitude). He wanted me to kill 3 Melar Smugglers at the local jump gate nexus. I already had one killed and tried to kill another one. But when i killed the second, it didn’t count toward mission progress.
What was unusual is that i killed him in motion (both me and him) and the debris kept traveling to the destination point… I would have expected the debris to stop where the ship was killed… Well actualy I am aware of the inertia, but that would make the debris continue off the map 
Other thing that may influenced this was that after the killing a clicked retreat. But Im just mentioning this just in case… But i retreat right after battle almost every time and this hadn’t happend to me yet…
I suspect as you say that by retreating as soon as you landed the killing blow you did not give the background systems enough time to register the kill. If you wait say 5 seconds before hitting the button, you should find it registers.
As for the inertia, if the enemy is moving, it has a pre-defined spot chosen, and will continue to that spot. When killed the image is simply changed as the reference needs to remain for the salvage.
Well, I believe i did wait like 3 seconds or so when this happened… But ok, I’ll try to wait a bit more next time, maybe it was too short period of time…
As for the inertia, I completely understand. And i actualy expected something like what you described. It’s not a big deal in the game merits, I just found it a bit funny But the main reason for mentioning it, was just to make sure it’s not related to the uncounted kill problem…
So anyway, thx for the quick response!
Just as a side note, iirc mission kills require at least 20% damage share in order to be registered. That is, 20% of enemy’s max structural HP (not counting shields) done by you in while staying in combat. If you damage an enemy, then retreat, repair your ship and finally re-enter, you start at 0% share while enemy might still be damaged.