It is impossible for us on a forum to tell what is "wrong" (if, indeed, anything is wrong) from these scans. I can tell you that I (as well as many, many others) could likely take those negatives and print them at several different contrast grades and/or light to dark ranges.
According to your account, the variable here is the FP4, as opposed to other films. Films are different. FP4 is a good film, but if your lab does not do a good job on it, and likewise does do a good job with the Fuji films, then use the Fuji films. I know you don't want to "waste" the film, but would you rather waste the shots and the processing costs?
I also agree with using box speed. Box speed in a camera such as you describe, with anything near normal development, should give a printable negative.