Not to sure about this my switch is offline with tx os, if your on your own cert backup I'm not sure what could be up with it.
EDIT ***
To unlock characters in Mario Tennis Aces, you need to participate in the monthly online tournaments. There's no character for June because the game released three weeks into the month. However, if you participate in the July tournament you'll unlock Koopa Troopa. If you play in the August online tournament you'll get Blooper.
Don't worry, if you're not into playing online you can still get these characters. For anyone who doesn't play in the monthly online tournament, the character will unlock automatically (after a free update) at the end of the month.
No idea whats up with you save unless modding the rank dose something.