Issue

Office 365 Nintex workflows are triggering multiple instances.

Resolution

Open the Nintex workflow causing issues in the Nintex Workflow designer. Navigate to the workflow settings in the designer ribbon and check the workflow start conditions. It possible the workflow is configured to start when a item is updated or when a specific condition is met. The workflow is most likely meeting multiple start conditions, causing the workflow to trigger more then once. 

Example: 

The workflow is configured to start when a item is created or modified. The workflow starts and the first action performs an update to the current item. The update causes the workflow to start again based on the workflow start conditions. The workflow start conditions need to be adjusted or the workflow design changed.