Hello,
Please provide more details about the issue, what exactly happens with the SD card, if possible, some screenshots as well, to have a better visual reference.
Do you make any configurations in regards to the SD card?
What exactly do you do to fix the card?
Lastly, a troubleshoot file with the issue present would be very helpful. To generate the file, access router's WebUI, go to System -> Administration -> Troubleshoot section and download troubleshoot file from there. The logs in the file might provide more insight into the issue.
Attach the file by editing your original question.
Best regards,