I got an odd one today. I purchased F, round-trip, GRR-ATL-SRQ-ATL-GRR in March of 2019. Receipt says F and until today itinerary showed "First Class (F)" Schedule changes today aren't flight times or equipment changes, but now the fare class listed on all segments is J. Still in first class, it's now First Class (J)". I thought J was international D1. Is it something I need to worry about?