I have experimented a couple of times with Fabriano and found it to be less than desirable. For me, currently, the two most trouble free papers are COT 320 and Revere. I don't like pre-treating since it's just another place for things to go to wrong.
On the other hand, Richard Sullivan has said, regarding clearing problems, "longer, stronger, hotter." My take on that would be, try mixing the clearing bath stronger, leave the print in longer, and perhaps heating it up would also help.
Boy do I miss Crane's Platinotype.