I've been looking at a one-way SFO-JFK-SJU on 30 November on flights DL315 (Delta One) and DL1859 (F). Delta.com shows award ticket availability for 95K miles (or 80K plus a bit more cash). However, when changing the search to pay with cash, that connection through JFK does not show as available in any cabin. Google Flights gives the same result.

This seems odd! Has anyone encountered this situation before?