Pokémon Sun and Moon has a glitch involving its Friendly Competitions. The problem has to do with entering one. People who are scanning QR codes to enter into and compete in a Friendly Competition before it starts have reportedly been unable to participate at all. (Thanks, Serebii!)
The Pokémon Company is aware of this Pokémon Sun and Moon glitch. The current remedy is to wait to scan any Friendly Competition QR codes. After one has begun, then it is safe to do so and enter. An actual solution to the problem is in the works.
Pokémon Sun and Moon is available for the Nintendo 3DS.