I think your problem is actually a very common one. Since you are doing restoration work here, I guess some more work on the realy coarse stones might help. You never know how beat up the edge really is,
even without showing chips and nicks the edge can be dead. Maybe that is the case with your razor; in some places the edge has just been knocked off.
I would recommend a thorough bevel setting, maybe with some coarse stones. I love my Shapton GS 500 for restoration work