Not sure if this goes here or on Sapphire's page. Anyway, the app seems to be unable to close properly or return to the home screen while the sysmodule Sapphire is installed. N3DS 126.96.36.199-U, Luma 8.1 with L2 and Clock, FS 3.1.2 and Sapphire.
Uninstalling Sapphire, which was tricky to do because I had to check the makefile to find the product code, instantly fixed the problem.
Edit: Needs clarification: Is Sapphire meant to be installed separately, or is it's functionality included somehow?
It freezes with me too N3DS 188.8.131.52-U, Luma 8.1.1 without L2 and Clock, FS 3.1.4 and Sapphire. So, I'm wondering is it still required.