Like Gail, I had a similar issue with Delta/Air France. In April we were scheduled to fly from ORD to CDG on the only non-stop flight of the day. The flight had been booked on Delta's website but was being operated by Air France. I had a Delta record locator number and knew both the DL flight number and AF flight number along with my ticket number. On the day prior to travel, I got an email from Delta with subject line, "There's been a change to your upcoming trip." The email had no details but was directing me to use the Delta website or app and enter my record locator number under "My Trips." When I did that, red letters warned me that the flight from ORD to CDG had been cancelled.
I went into the booking feature to see how I might get to CDG on an alternative flight and could no longer see any non-stop flight listed, which seemed to confirm the cancellation. There were some options with layovers and I called Delta customer service with the intention of working with an agent to book one of those. While on hold, I received an email from Air France notifying me of a "modification" to my flight, now departing ORD at 19:10 instead of 17:10. What? Still on hold with Delta, I tried to check into the flight using the Air France website. I got an error message telling me to contact an agent. While remaining on hold to talk to the Delta agent, I checked back under My Trips on Delta's website. It still said my flight had been cancelled.
When my call was taken, I related all of this to the Delta agent. He put me on hold and when he came back, he said that it was a 2 hour delay, not a cancelation. He said that when Air France has a delay of that length, they assign a new flight number to the flight, and this required that our tickets be re-issued, which he'd just taken care of. He admitted that when this happens, the Delta website "lags behind" the Air France website.
I was satisfied that I had a secure flight, but contacted Air France customer service because of the "contact an agent" message I'd gotten when I tried to check in. The Air France agent confirmed the two hour flight delay.
Within a few hours I was able to check into my flight on the Delta website. I kept checking back under My Trips on the Delta site just because I was curious to know when this "lags behind" issue would be resolved. Interestingly enough, despite the fact that I was checked in, each time I entered my record locator number under My Trips, it still had a red lettered message that my flight was "cancelled." At the airport the next day, through security and waiting for my flight, entry of my record locator number under My Trips STILL said the flight was cancelled!