This malfunction isn't because you did something wrong in particular.
I have experienced something similar recently.
My SD card was completely in a locked state.
It was showing as write protected, just like you.
Which means I couldn't add or delete files to the card.
I couldn't even format my SD card or using Diskpart. (Windows and Linux environment)
Out of Curiosity I also gave Decrypt9/Hourglass9 and Gateway launcher a try to format (creating emunand) the card.
It just left all the files just like before and act like nothing has happened.
I know this isn't funny to hear but, like other members already told you, your SD card is dying.
Firstly I strongly recommand you take a backup while you still can. (even emunand if you get one).
I luckily took a backup from all my files on the SD Card before, but my emunand is gone forever.
Than try to format your SD Card to FAT32.
If that fails, there isn't much you can do,
just buy a new one.
I'm sorry to disappoints you.
If your titles doesn't shown up correct on your Nintendo 3DS system, first insert your SD CARD in your Nintendo 3DS.
It will make a new folder in the Nintendo 3DS folder on your SD card.
Copy manually all your data from the folder with a long text from your Nintendo 3DS folder from your backup,
and copy it over to the folder with long text in your Nintendo 3DS folder folder on sd card. (The sub folder in the Nintendo 3DS haven't the same name, which can cause that tiles aren't shown up correctly.