Is this specific to international flights? Because when I flew EWR-LAX last month I waitlisted and still received upgrade offers (in fact, I took one). I just placed myself on the waitlist for the EWR-MAD flight and now I can't see any more offers, including for my return flight which is PMI-EWR (and there was previously an offer for $3600). Wondering if I should cancel my miles + cash waitlist bid and hold out for a decent offer.