Retroarch has a known issue with Luma and the way Luma handles crashes. It always crashes for me, regardless of the core I load. Since Luma was updated last (Luma3DS version 8.1.1), Retroarch and NTR CFW are the only homebrew apps still crashing for me.
It's gotten to the point that I prefer the standalone SNES9x and VirtuaNES by bubble2k (god I wish he'd write a Genesis emulator too!) over Retroarch because of a consistent easy to replicate crashes. Basically do this: Load Retroarch, load any core, load any game for that core. You've got a 50/50 chance of actually playing the game and not seeing it crash. If by chance it does load the content and you get to play, it is GOING to crash on Retroarch exit. So, load Retroarch, load core, load content, play for a bit, tap bottom screen, select "Exit Retroarch", CRASH! Everytime. Guaranteed.
Nothing you can do but nag the RA guys to fix it. Since the issue has been present basically forever, I'm not holding my breath. Luma's newest builds got a little more strict on the way it handles crashes (because the CFW devs are depending on people to fix this in their homebrew, where it needs to be fixed), so the issue hasn't been present until Luma3DS build version 8 and beyond.
If you MUST use Retroarch, my suggestion is to continue to use A9LH+Luma3DS 7.1. If you have a NAND backup from this setup, you can use GodMode9 to restore that NAND successfully to remove B9S, restore A9LH, and restore Luma3DS 7.1. I have done this and confirmed with astronautlevel that it works fine. Any games/updates/saves will need to backed up and restored afterwords. Keep in mind that Luma3DS does not support A9LH anymore and you will no longer receive support or updates for Luma3DS. Of course, the safest option is probably to wait until Retroarch fixes the issue. (And they may have in their latest updates, I'm not sure.)
For what it's worth: My experience with PCSX-ReARMed for 3DS has been pretty extensive. I've gotten a lot of games to play fine (~50-60 fps), and a lot more to play tolerably (~30-45 FPS). In all cases, audio must be disabled in RA settings for any game to load properly. Also, BIOS is important. Use a clean BIOS file (preferably SCPH-1001!) you know is good. (Meaning MD5/SHA1 hashes match the official!!!) Other than that, there isn't much else you can do. Not all games are going to play (Final Fantasy games are especially horrible), and those that do are going to suffer badly. You are much better off emulating on any other handheld, including any Android device. (For real, I have an old LG Optimus that runs Android 3.4 and plays PSx almost perfectly on its very tiny screen lol)
