Here an extrat from: https://docs.mendix.com/refguide/version-control/#3-5-commit-changes-to-team-server-repository

2.6 Conflict 

A conflict occurs when two versions of the app cannot be combined automatically. This happens when the same document has been changed in a Studio Pro working copy and a committed revision and these changes cannot be reconciled. These are some examples:

• The properties of a widget are changed in the revision and the working copy but to different settings
• A document is moved or deleted in the revision but has been changed in a different way in the working copy

When a conflict occurs, a developer has to intervene to decide how it should be resolved before it can be committed to the Team Server as a new revision