Event Scheduler Portlet > View Group field > Some Groups Displayed Are not in the Group List

Navigate to Activities tab > Scheduler portlet > View Group field.

In this dropdown field, some groups displayed are not found under Lists > Relationships > Groups.

This happens when Team Selling is enabled (Setup > Company > Enable Features > CRM > Team Selling). The other groups displayed are the sales teams which can be found under Setup > Sales > Sales Teams.