Funny enough… just 3 days ago, i praised SanDisk for their cards:
I guess one of my cards overheard me or something… because today my first SanDisk card decided to just give out randomly 
No device i own was able to read the card at all anymore (PC, Mac, Polyend Devices, other SD enabled devices). The card was close to 3 years old and wasn’t in-use for a while.
So i figured this is a good time as any to tell/remind you all:
Backup your data regularly
That is all folks, have a good day! 
Excellent advice!
I also noticed that you mentioned that the card was not in use for a while. That can be a contributing factor. It is important to note that all flash memory (whether cards, SSD, etc.), needs to be powered periodically to refresh the state of the memory and recharge the capacitors. The newer the card, the longer the charges hold up - when new, the capacitors should hold a charge for a few years at least. Of course, I have had cards not powered on for over a year and they have still worked, but it is best practice to periodically power the media for a while. I think manufactures should mention this more often. But they are probably assuming that people are at least periodically using the media, if not constantly, so it is of no concern.
But of course, the best protection is multiple backup copies - no matter the media type!!
Michael…
Okay I’m backing up TODAY. Thanks 
I had the same thing happen with my factory Tracker+ memory card. Neither my Mac or Tracker+ could read it. So I bought a larger San Disk card.
My factory card somehow got corrupted and became unreadable when I was dragging samples to the PT from my Mac over USB. I was able to reformat it on my Mac and start over, but switched to the San Disk moving forward.
As a precaution to this happening again in the future. I’m keeping a mirror of the contents of my card in a folder on my Mac HD, and using that as a backup periodically.
I brought my PT on vacation with me, so I mirrored the contents of my cards before I left, so I have a backup with me while away. 
Independently from the brand or age; backup is a must
Also anything may give up and break; I had cards dying after a week, simply because of a bad sector written over and over, and that sadly was on the MBR so there is no way out when it died and there was no free blocks left to be replaced.
After many accidents I just bougth a NAS, got 4 disks of 5 TB each and use those in pairs to save my stuff… Every time one break I replace it. Sound excessive, but it is peace of mind for all the stuff I want to save.
I do the same. Have a Synology NAS with two 12 TB drives in Raid 1 (Mirroring) mode. Use it to backup everything in the house (three laptops, Polyend Tracker Mini and Play, various other musical devices that use SD cards, phones, etc.). Ironically, I have never had a SD card or anything else fail on me, but I do have backups in case it happens.