Dude, I was in the same situation as you. I have a Nintendo XL (OLD3ds) in version 9.2. So I did not have to downgrade to 9.2 and keep all my saves and data Nand (Mii Plaza, Saves, etc.) During the process to install A9LH.
I had the same problem after reinstalling the backup of Nand. The Eshop not connected, giving 022-2634 Error. this is error is caused by an authentication duality in the Nintendo servers. But that you already know, so ...
After much reading, I ended up using two
tutorials, and elaborated a method that served to me without the loss of my 9.2's original backup. (Original A9LH):
1. Remove the SD of your device and Make a backup of your entire SD using Win32DiskManager program. Create an SD image and keep safe.
(If all goes wrong, just restore this image to your SD)
(For some unknown reason, the Emunandtool did not work because not detect my SD)
2- Download the last version of TinyFormat, and install in the Emunand Using FBI.
3- Make sure you has in files9 folder backup of Nand (9.2) made during the installation process after A9LH activated.
(The name of my file is NANDmin_sys.bin, referring to the FILE ORIGINAL 9.2 DONE BEFORE INSTALLING THE FIRM 2.1)
4 Go to an Internet Browser (out of 3ds), visit Miiverse Site and try to log in, if returns the error during login process, no problem. This will make an authentication of your NNID *
* (This part may be a coincidence, but worked for me)
5. Go back to his >> 3ds Tinyformat >> format your device and reconfigure it.
(3ds will Return to Emunand in version 9.2)
6- After Reset On, Turn off the device and Open Hourglass9 from arm9loaderhax by holding Start on boot
- Go to "SysNAND Backup / Restore ..."
- Select "Restore SysNAND (keep a9lh)"
- Confirm and restore from NANDmin.bin (The name of my file is NANDmin_sys.bin, referring to the FILE ORIGINAL 9.2 DONE BEFORE INSTALLING THE FIRM 2.1)
7- In the newly applied version, go to Settings >> Nintendo Network Identification >> and make sure your id is logged. If he gives notice asking to update the Firm, return to the main menu.
8- Try to log in Eshop. If ask to update the firm, go to Settings and make the upgrade.
9. Complete the installation procedure for the FBI via Banner Injection and try to enter the eShop.
If all goes well, your eshop will be functional and your data intact.