When creating an Event Series on a Multi Event product there will be a default set of 10 for the maximum amount of events you can create in any one series. If you wish to increase this please follow these steps from the Admin menu:

  1. Click SettingsĀ > General Settings > System
  2. Scroll down or search for the Group Op Multi Event Max Events box
  3. Increase this to the require maximum of events
  4. Click Save