Hi there,
so as a scientist I would recommend a small experiment to make sure its not truly an infection. make a small starter using DME or just sugar and add some of your "sample" to it and let it grow. if it should truly be infected it will grow and you know for sure.
But, most likely, its the oils from the hops which react to your water chemistry. If you have a slightly higher Alkalinity in your water this will lead to this "fall-out" of the oils of the hops on top. Make sure your water is nicely balanced in its components.
Hope that helps,
Cheerio and good brewing.