I have this problem every once in awhile with Fomatone. I suspect, but do not know for sure, that I somehow contaminated the paper with fixer or something else just before development. Next print, its gone. Maybe it is the occasionally defective sheet of paper, I don't know.
But I do know that Rudman's admonition that poor darkroom hygiene will show up when lith printing is oh, so true. I have learned to keep my hands clean while handling the dry paper, and never, ever, touch the paper with my hands after it has gone into the developer. I put it in face down, turn it over with tongs after 1 minute, and develop the rest of the time face up with constant agitation, never poking at the paper with my tongs (or anything else.) I use separate tongs for developer, stop, and fix to avoid contamination.
Regarding your contrast issue, I find that when I get a muddy looking print I need to back off on the exposure time, which will necessitate an increase in development time. 1/4 or 1/2 stop is usually enough to give me nice, clean, bright highlights and punchy, dark shadows.