Twitter card does not work anymore after a certain time



My website is validated for the Summary Card with Large Image (As an instance this page

When I share my page on Twitter the card works as expected but after some time my cards are no more displayed
For example these tweets :

Is there something wrong with the way I provide meta data or anything else?

Thank you for your help

PS : You could not that @nytimes tweets with cards have the same problem



Sometimes it works, often it does not work. Do you know if there is any problem times to times?