Problem transferring files to sd card

I’m trying to transfer files (in this instance music files, mp3 and flac) onto my sd card. So I have tried various routes and all fail. I have taken the memory card out and plugged it into a card reader, and then copied the files on my pc, I’ve also connected the fairphone by cable to the pc, and also wirelessly (but the latter wouldn’t work for some reason, although it has done before). Anyhow, this is the first time I’ve tried transferring files onto the sd card from my computer. In Windows Explorer I have copied and pasted the files I want, and it took a while transferring them. Then when I put the card into my fairphone, neither the folder nor the files were visible in the file manager, and when I put it back into pc, they weren’t there either!

I’m really confused. I’ve tried connecting the fairphone with the usb cable and it gave me the message in explorer that it could copy the files but that they might not be recognised, but i copied them anyway. After the 5th go, the files copied, and could be viewed in the file manager on the fairphone, but when I tried to play one it played at super-speed, (one track in several seconds), and then when I rebooted the files, all but one folder were not visible. This is very puzzling. Can anyone advise what I can do?

Very odd situation.

This shouldn’t be the problem, but I have known issues to be caused with Windows when you disconnect either the SD or phone without ejecting first. So are you ejecting the device/card from Windows before you unplug/take out?

Another thing you could try is to reformat the card in the Fairphone and then try again - formats can be a problem with larger cards