What is causing these streaks?

If it's not on the original artwork, I would first say static.

I don't think it's dirt or you'd see droplets here and there.

 

lines

It might be something simple with just cleaning under the printhead or lifting your printhead height.

 

it looks like something is dragging on the printhead. Try cleaning it.

 

You must be printing in Bi direction as the lines are going in both directions of the graphic. Is yours a cutter as well? I have had a fuzz or hair get caught on the cutter blade and I cleaned the head many times and funny it didn't help. Now I remove the blade tool when I just print just to keep that from happening.

Although with a hair or fuzz you should see it in all areas and not just on the darker blue unless the amount of ink that color produces is just enough to be the only color that touches the debris.