Generation created teams you did not set up, or put two unrelated players together.
Cause: In a doubles division, any player still without a partner when you generate is paired automatically. If one player is left over after that, they are entered as a single-player team.
Fix: Set partners deliberately before generating.
Open the Players tab.
Use the pencil icon on a player to edit their profile and set their partner.
Clear the affected rounds and generate again.
For a large roster, a spreadsheet import with both partners per row is faster than pairing people one at a time.