Incremental mode can't be used with short living branches and also in the first analysis of long living branches.
In a short living branch, we are already analyzing a diff (compared to the target branch) so it doesn't make sense to consider an incremental mode.
For long living branches we need to do a first full analysis so that all components and issues are created for it. It's a similar to the obvious requirement of having to do a full analysis of a project before using the incremental mode.
To make it easier the implementation and to set automated builds, it's probably best to ignore the incremental mode when using any kind of branches.