I was having problems yesterday playing games in local multiplayer with my friends. After playing any game for probably a minute, connection would be lost. I don't know if it's related, but the only change I made to my system after I was able to play before was turning off New 3DS CPU on Luma3DS. In case it's relevant, I have a New 3DS XL with Luma3DS installed while my friend has an unhacked original 3DS. We both have the latest firmware update installed.