The Space.com article Strange Sky Spiral May Come from Secretive SpaceX Zuma Launch shows images from this Tweet and this tweet, the second of which was posted by Dr Marco Langbroek (@Marco_Langbroek):
Palaeolithic archaeologist (PhD), spy satellite tracker, asteroid discoverer. Tweets about space, archaeology, astronomy & other interests. Asteroid (183294).
There is a lot more Zuma-related orbital mechanics Dr. Langbroek's twitter (and extensive blogposting) as well.
Is this unburned propellant, if so, why would this need to be done, and in any event, what gives it this particularly distinctive shape?