Navy on white base - weird result

[anunnakiscreener]

This is a new one for me and I've been printing for years. Imagine a white base that was printed P/F/P/F and small navy circle on it. The navy resulted in vertical dark and lighter navy alternating stripes about 1/8" or less wide. Weird. Tried everything but stripes remain. Was there an issue with the screen perhaps from a previous image? 156 mesh on both.