[2023] Neptune Junction no drops?

You earned the Chroma Chassis Blueprint as a junction reward in the past (a very long time ago), and then you sold the blueprint in a batch along with many other things.

It's important to review the "Sell" window carefully 😅

Junction rewards are only earned once by playing the Junction.  Like most unique rewards,  now that you've earned it once, you can get a new copy of the Chroma blueprints from Cephaon Simaris for a cost in Standing points.