I was upgraded at the gate on HNL-> JFK from Main to D1 as a Platinum with AmEx Reserve.
This happened in November. All other Delta flights (to LAX, DTW, ATL) and even FC to SEA had zero seats for upgrades, and JFK flight had several free D1’s.
I think, of all flights from HNL only JFK is not a hub, so there are fewer upgrade-eligible elites. You compete with passengers paying for D1