Hmm, yea, it does it to mine too... Weird! Maybe its cause it takes up too much system resources but this is just a guess... Cause u cant use the miiverse or the internet browser while you are playing the demo and that will be in the full version as well due to a lack of system resources/hardware so maybe that has something to do with it but again, not sure loll. It looks like they really sacrificed a lot to achieve that 60fps on the 3ds
http://www.nintendolife.com/news/2014/09/standard_3ds_consoles_will_have_limited_online_functions_when_playing_super_smash_bros
PC Specs: CPU: 7800X3D || GPU: Strix 4090 || RAM: 32GB DDR5 6000 || Main SSD: WD 2TB SN850