Have you tried to:
--reboot your phone?
--reformat the SD card?
--Verify that the SD card is compatible with your device?
I was having the same issue with my last SD card. I had moved it from one phone to the next for several phone swaps. Reformatting did nothing to help, but once I got a new SD card that was compatible with the faster processors on my phone, it has not been an issue.
Welcome to AF! please consider joining our community!