A result concentrated in one rack gives different information from every item remaining dirty. Loading, clearance and the exact appliance arrangement need to be considered.
Understanding this situation
Check for obvious shielding by large pans or boards with the machine stopped, following the manual. The location does not identify a particular pump or spray component by itself.
A useful next step
Describe the affected positions, programme and type of residue. If a suitable load still shows the same pattern, arrange assessment. Do not remove wash components or run an open-door experiment to see where water is spraying.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.