Lots of flavorings have bad things in them. The things that are used to replace diacetyl are sometimes as bad or worse then diacetyl. I thought flavorart was switching away from using any diketones (I think this includes diacetyl) in their flavoring, but I'm not sure about this. I'd contact FlavorArt for this kind of information. Finding out exactly what makes up flavorings is nearly impossible.
In general, rich 'buttery' flavors use diacetyl. The quantities are tiny. Several vendors produce liquid that is labeled as diacetyl free, so if you want to avoid it, you probably can. Though you then have to believe the liquid vendor and the vendor has to get accurate information from their flavoring supplier who often has no idea what their flavoring is made of.
In many people's opinion (including my own) this is not something to be too concerned about, at least not more so then other flavorings. I'd be more likely to switch to vaping only unflavored liquid then to try to avoid just this stuff. But by all means, do some research and decide for yourself what level of risk you are willing to live with.