TN said one card failed, and that he lost three clips from it, video at 4:20.
That was not a new card (Lexar, pre-liquidation) so presumably it's been used before without problems, and he formatted it in the EOS-R. So far so good, but it would not be the first time that a new camera has had problems with certain cards at launch - presumably because it would be impossible to stress-test prototype cameras with every conceivable make, model, size and speed of all cards ever made - but it's always quickly fixed with firmware.