longcat
I have purchased two of these 64gb sd cards and used them in an Android phone, and in a video recorder.After about 3 months usage in my phone, the card would randomly unmount and it took many remounts or reboots to get the card to work again.  Eventually, it stopped accepting writes at all, and couldn't even be formatted... although I could see what was on there.I repurchased the card, and after a couple months, the same thing happened again: random unmounts.  I moved the card to a video recorder, where it worked for a while... but even with a different usage pattern, it died again.I have had no problems with 32GB cards so far.  I'm staying away from this generation of 64GB cards.----EDIT----Getting these cards RMA'd was quick and easy.  I had a Lexar 128GB SD card die too, and I sent the cards in all at the same time.  I haven't gotten an update from Lexar, but I got updates AND my replacement from SanDisk.  Supposedly there was something fixed in this new card revision.  I hope so.