I had this today as well,  on one of my tarot missions - the Nurgle chaos engine I fought had its entire central body turn invisible and you could only see its head, weapon and legs, very nasty game braking bug.  I've also had the entire screen have massive graphic glitches where I had to restart the game to fix them.

I realise that its hard to get all bugs - but there are a lot of bad ones in this game at the moment.

I know that this is one quite old thread as of now though. But I have to say that this bug is still present to some extent in some of the Missions. I didn´t take any pics, but I wished I did though. In fact I wished I had some live footage of it instead.

The thing is that the only thing I can actually see is the weapons effect. Yes, this means I can only see the actual effect of the weapon itself. Like Flamethrower I can only see the flames sprouting out. I can see the Plasma Ray from a Plasma Cannon, or the laser from a Laspistol/gun. But the mobs who are using it is gone. It is however a very rare thing that does pop up. I think it is the 3rd or 4th time I see it, and last time was today in a Hunt Mission within a Snow & Ice terrainy.

But I do not remember what system/zone this was within.

No, that is exactly what I can not recall. Also because it is not a very common thing.

But if and when it does pop up again, I will remember to at least take a pic or two.