External SD card no longer able to be read on CM11
How old is your SD card? Does it work under stock? If it doesn't work under either, I wonder if the SD card is going bad? How long have you had it and do you do a lot of writing to it? If so, then the card might be going bad as SD cards have a limited lifespan. The more you write to it, the shorted the lifespan.

Do you have another SD card you could try? I would also do a chkdsk on it to see if any bad sectors are found. If so, time to ditch it and get a new card.