I think they are what ENFER wanted Sophons to be. They are genetically engineered Sophons that ENFER created in order to be more aggressive and warlike.

Mazros and Sophons aren't a markedly different species as in dogs and cats, but more like German and Australian Shepards. 

Pluvinarch has also has a point, that the Mavros on Illumination are possibly genetically engineered Sophons, and/or the Mavros really are just aggressive Sophons regardless of their description and thus the Sophons on Illumination would be more aggressive Sophons. 

I never thought of that, that they could just be modified Sophons. My problem with this theorie is, that I believe, that the description of the factions and minor factions are really true. If a living thing doesn't belong to the same species, it is so different, that it can't breed with this species. The Sophons and the Mavros differ more than a German and Australian Shepard, which are different breeds. It could be, that ENFER was so advanced, that he could modify the Sophons a lot, so that the modified Sophons don't belong to the same species anymore. I believe, that it was the opposite. Perhaps the Mavros infiltrated the Sophons and manipulated ENFER. What goal did they have? Maybe they wanted to change the Sophons, or they only wanted to spread chaos. 

I read the minor faction description another time and I noticed, that it only states, that it indicates, that the Mavros are a different species. It is a really vague description and so some points about different species in my previous post aren't as significant as I thought.

Yes, you are right, that it is a grey area with different kinds of classifications. But looking if they can breed plays an important role and is a good indicator. But defending this system isn't what I wanted to do, because we don't get any information, that they can or cannot breed. My question was, if ENFER can modify them so heavily, that they don't belong to the same species anymore, or if we have to come up with another theorie.

Markedly different species can still breed as long as they're within the same genus/familial tree. Hence Dragars point about humans (though he simplified it a bit) as modern humans are the combination of about four different species (Homo Sapiens and Neanderthals the most common, and then another species from Asia, whose name I cannot remember, and an unclassified fourth species whose DNA is found within people of, I believe, Eastern European origin) 

So Mavros and Sophons could be different species (though their physical bodies, exosuits, and extreme intelligence state that they're probably cousin species) but they can probably still breed together. There just isn't a game mechanic for interbreeding similar species, hence why you can't see it in game. 

So I think ENFER had some role in Mavros society, though I very much doubt ENFER created them. This points to that the Mavros is a subsophon species that ENFER might have preferred in comparison to the Sophons who, more or less, reject ENFER. 

I do not think the Mavros tampered/interfered/infiltrated ENFER though. 

However, this could also just be a game bug and Mavros were put in instead of Sophons, or that the DEVs used it as a cute little easter egg, or possibly the prelude to a Sophon/Mavros minor faction quest. 

But yeah, I think Mavros are just a cousin species of the Sophons with a markedly different culture and society but similar/same genus, hence why they would be present on the Sophon only world of Illumination III.