Welcome!

You're on the data centre as me, and because the majority of players are Japanese, it's really important to have your duty finder set to include speakers of all languages and not just the default English. Otherwise it's trying to gather a party for you out of a small subset of the players actually available at the time.

When you open the duty finder, there's an Options button (gear icon) up in the top-left corner. Turn on the other languages there.