Oil residue on top of beer/graff after racking to keg

[Brewboz]

So yeah I cleaned my keg with soap and water. Rinsed very well then star san. then racked my graff into it and there was this residue on top of it.. I have brewed about 10-15 batches of different things and never noticed it. Before and while I racked into the keg i looked into the fermenter and did not see any kind of oil slick. I had taken a sample with a hydrometer did not see it there I sprayed out the measuring cup with some star san and dumped the sample into and found the same oil slickerdoodle. What is it? Does star san do this and I have just never noticed? is my beer infected it tastes great in the sample tho it does smell uh tart~ I used Nottingham doubt that would make a difference and stuck to Brandon's recipe. its crystal clear just after 12 days with one rack. Idk I still kegged it. Anyone else seen this same thing?

 

[Lefou]

Star San is one part acid and one part surfactant.
Not sure if you're seeing the "surfactant" remains that could result with the interaction of hop oils.

Did you hop your brewed graff at all? This could be what you're seeing.

 

[Brewboz]

I did hop the beer but not much just what the recipe asked for