I thought you might be interested in my experience using my "Carte Vitale" recently. My husband and I are British and became resident in France officially just over a year ago in 2018. We are retired with full NI contributions in the UK and were therefore able to obtain our Carte Vitale for medical care in France using our S1 form which covers 70% of medical care paid for by UK.
All went well, last year we had an appointment and duly registered with our local doctor. However, this year in August 2019 after visiting the doctor I was given a hospital appointment and also sent to a laboratory for blood tests. At the hospital they informed me that there was a problem with my Carte Vitale and that I will have to pay the full price for the examination. A few days after I received a letter from the blood test laboratory saying that I would have to pay the full amount as my Carte Vitale had failed to reimburse the 70% to them, even though it registered my details at the time. At the pharmacy for a prescription, the card also appeared to be playing up, although they let it go through at the time. I had twice in the last year updated ("mettre à jour") our carte vitale at the pharmacy, so did not realise there was a problem.
I got onto the website "https://assure.ameli.fr" and sure enough all our details were there and I was able to use the site and look things up, so I thought I will look at the attestation and update it. It was then and only then, did it say there was a problem with our cards and please call CPAM.
My husband and I ended up back at the CPAM office in Le Mans where the young woman there was extremely helpful, she was not sure why it was not working and when she tried to print off our attestation it said that the cards had been cancelled on the 29th March 2019. This of course was no random date and when she spoke on the phone to check with another office they told her it was due to BREXIT !!, It was discovered they had been cancelled the day the UK had been due to crash out of the EU !!!!
Not only was this extremely worrying, but I wonder if other British people may have been subject to the same thing and are totally unaware of it. You may want to do an article on what has happened. Now whether the decision came from the UK or was a clerical error or a definite decision on the French administration I have no idea.
However, I would add that the young woman sorted it all out for us and said it would be corrected and put right immediately, to wait a couple of days and then get back on the website in order to print off some new attestations which thankfully we have done, and to go back to the pharmacy to get the cards updated as well. I imagine the only way people can find out if they have been affected in the same way, is to try printing off an updated version off "attestation de droits" on the "https://assure.ameli.fr" website.