One isolated incident reported on squidboards.
Them appearing in your plaza is the problem (game softlocks, note plaza loads on title screen
). Technically a splatfest could fix that as only people who make splatfest posts will appear in your plaza.
I believe you avoid them appearing in your plaza by them leaving a room before you leave. Not sure what happens if you disconnect.
Alternatively if you're using an external drive copy your save to the external drive and restore the save from the system memory should anything happen. If save is on external drive that one is the one the system reads/writes so the system memory acts as the backup. This can also be used to abuse ability re-rolling (do a few re-rolls fail to get what you want, restore backup to try again).