Use the latest
stable build of Luma (v6.6) and try again to boot into 11.3. The nightly isn't needed since it was a pre-fix for HBL on 11.3, now that the payloads are updated it's not needed. I would
highly encourage noobs to stop using the Luma updater. Yes it may be easier but nightlies aren't for noobs who can't troubleshoot themselves (no offense) they only cause more problems then they solve with their buggy nature. Anyone having problems needs to do this:
If you installed A9LH Between March 2016 - October 2016 you need to update A9LH by going here:
https://3ds.guide/updating-a9lh.html
If you installed A9LH recently you should be fine.
Now go here
https://github.com/AuroraWright/Luma3DS/releases/tag/v6.6 and replace the "arm9loaderhax.bin" on the root of your SD card.
Now your DS should boot fine, and you can update to 11.3 if you haven't already.
Now go here
https://github.com/yellows8/hblauncher_loader/releases to download the newest release of HBLL (HomeBrew Launcher Loader) and delete your old one using FBI.
Install the new one and boot it while holding "X" to update to "Hax 2.9" and download the new payload automatically. (You must be connected to the internet).
And that's it. Good luck to you all.