Error code 001-0502 on Friends and can't connect to multiplayer (3DS)

Hi, connecting to the Friends list from my New 3DS used to work fine, along with entering multiplayer mode for games such as MK7, however, in the last 2 days this has no longer been the case and I can’t connect to Friends or multiplayer mode on the supported games (tested with MK7 and Mario Maker). I have another New 3DS XL on Pretendo that works fine and can connect (for now). I tried using my mobile phone as a hotspot and could connect on my New 3DS (not XL), making me wonder what could be the issue here.

Any help is appreciated!

Duplicate of Error code 001-0502