If a model transformation is run multiple times, it is possible to select a target model of an already existing model transformation instead of generating a new target model. Changes to the models that can be made independently in source and target can result in conflicts that are not automatically resolved during model transformation.
If you selected the Perform interactive merge option when running the transformation, the conflict model is displayed with the changes and possible conflicts being marked. At the same time, suggestions for resolving the problem are offered.