"He who marches out of step hears another drum." ~ Ken Kesey
did you anti-alias your raster? if so the printers will see the soft edges and think it's white.part of the issue with DTG is the faster you print the more dots in the image(usually).I do not recommend printing 50/50's dtg. The prints just aren't as bright and the fabric messes with it more. Part of my issue with Kornit printers is the pretreat doesn't mat down the fibers so you do get more fibrillation since there is nothing but liquid that touches the shirt.