I just set up my sons new yoto mini and per the instructions for downloading them for offline use, inserted each new card for a few seconds until the app recognized it and then removed it. The instructions say that the player needs to be on, plugged in, no card in or playing any content and online. Our player is all of those things yet these cards are just sitting in "not downloaded."
And yes, I have tried inserting one of the cards back in for a second and it WILL pop up and say "downloading..." but then after a few minutes of the card being removed again it will pop back down to the "not downloaded" list.
