His suggestions there are what I already do, so maybe I'm just getting really unlucky? I guess I'll try some new MAC addresses that I haven't used before and see how it goes. I didn't mind only getting 9/10, but only getting 8/10 sometimes isn't enough to fully grow my flowers on Flower Town. It's not a huge issue, of course, but it's a bit annoying.
EDIT: That seems to have done the trick! Looks like I'll have to add some more addresses to my list in order to avoid future issues. Thanks!
I had that problem last week. This is what worked for me:
1. Go the Mii Plaza settings and turn off StreetPass and SpotPass.
2. Save the settings and exit Mii Plaza.
3. Go to Mii Plaza again and turn StreetPass and SpotPass back on
Once I did that, it started working again!