How did you process your 5x4? Did you use a Jobo drum? If you are doing rotation processing then you need to use a pre-wash. I was taught this may years ago by a former sales rep for the Jobo distribtors. He told me the single biggest mistake people make is not pre-washing for 5 minutes before development.

I've always used a pre-wash with my Jobo drums, and have never had any processing marks using any format film from 110 to 5x4

As for stabilizer marks - this can happen even with machine processing. We used to use film cleaner to clean the odd stab mark we got on our films. I can't remember the cause, but I know from experience using a drying cabinet and warm air helps avoid drying marks