I never double coat VDB when using Stonehenge. My paper is from the old mill and I understand the newer stuff is different and many do not like it.
I agree the streaks have to do with fingerprints.
Your exposure times seem excessive. Are your negatives that dense or is your printing frame too far from the UV source? Tests as spelled out in the Post Factory Journal indicate that with UV fluorescent tubes essentially no separation between the frame and the tubes is necessary. Mine are approximately 1/2" and do not produce banding.
Exposure times are usually along the lines of 13 minutes. The drop of 2%Potassium Dichromate makes the exposure longer than it would be without it but gives it a nice contrast boost.
Exposure is by BLB flourescent spirals - 60 w equivalent. I have six of them. They are about 3 inches from the paper, set close together. The exposure is even and consistant.
I started double coating because I wasn't getting good density in the shadows. One coat for me looks washed out but I understand that everyone's process is slightly different - depending on, well, every other variable.
Lostfocus, just drop the practice of adding dichromate into the coating solution; see this for an effective method of contrast control:
(Thanks much to Liam Lawless and Sandy King for researching/testing and making this information available.)
BTW, I would try to find ways to increase the negative DR instead of fiddling with the emulsion formulation; Vandyke works best unaltered.
I'll have to try that. Right now I'm using premixed solution from Bostick and Sullivan.