I was very pleasantly surprised with a free up on a LAS-JFK flight back in Dec, especially since it was a Sunday night redeye & I was headed straight into work upon arrival.

Running a bit late to the gate, I wasn't really sure what, if any, issues there were with the flight? Some other data points, fwiw..., I am Mosaic, paid with points but iirc, not anything out of the ordinary for a Sunday night flight. Also, I know at least one other Mosaic also received a free upgrade on that same flight