Same thing here, for my early July LAS-MDW flight. They moved me to a much later flight on the same day. If I try to use the change function through the link in the email, the earlier flight does not show up as an option. However if I go in to try to buy a flight from scratch it does show as available, but the points price has increased by about 3,300 points (nearly double the very low fare I originally booked). I haven't tried calling to see if they would move me manually back to the flight I originally had, since I'll probably end up just canceling anyway due to unrelated issues.