Hi,
There is a difference between the Project Roles, and the App Roles. For all nodes you can have different node permissions. The technical contact of you app can set them.
https://docs.mendix.com/developerportal/collaborate/app-roles
So even though you and your groupmate might seem to have the same roles, they can still differ, also for different nodes. I suggest you to contact the technical contact to request the same level of permissions.