There is a fix

What may have happened is a9lh has borked itself. The optimal way to fix this is to use ntrboot to put boot9strap (better version of a9lh) on your 3DS. A compatible flashcart will set you back ~£15 but you may have one lying around. For more about ntrboot, the card you need, and how to do it, visit https://3ds.guide/ntrboot