Thanks for commenting in about using the same system/setup. This seems crazy as to why the card stopped working on the old3ds w Luma, but my n3ds sysnand 9.2 (GW 10.x emunand) it still works...
When you start up, does it show 11.3 or something else? I have no emunand setup on the O3ds/Luma system. Just trying to isolate what is stopping the card from being seen.
Forgot to ask, what is the FW/update versions you have installed on the DStwo card? Maybe mine is off, but I haven't seen any updates on the site since like 2015 or something for it.