As a datapoint, departing CDG a few days ago ran into the same issue. App wouldn’t check us in, just kept a loop of error messages with the occasional “We’ve found your reservation, but check in must be completed by AF” (even though we were on solely DL metal).

Didn't attempt to check in via AF website. Just got to the airport early and had no issues checking in at the DL counter. The agent was very confused where our final was (ANC) and actually applied an international-international purple tag that, I didn’t find out until we landed in the US, actually said not to send to customs belt in the US! It said to transfer to the next international flight. Thankfully that did not happen, and we were able to claim and re-check as normal. So, lesson learned, watch the CDG contract/AF agents.

Even more amusing when landing in ANC, one of our three bags did not appear at the carousel, despite receiving the “bag on plane” scan departing SEA. I went to the baggage office and my bag was sitting there at the desk. The agent was very confused how it got there as apparently the baggage claim tag on the bag had gotten ripped off. (Must have gotten snagged on a belt loader somewhere). She said she didn’t know how she could officially release it to me. I showed her my name on the bag, my boarding pass, my AF-issued claim check, and even pointed out the little white sticker from the tag that had disappeared was on the side of the bag, matching my claim check number. To which she replied “Oh wow! I never knew those little stickers had numbers on them.” I explained they were a backup for exactly this purpose. She then released the bag to me. I swear agents are getting less and less training and we, as frequent fliers, know more about the system than they do.