The detergent needs to be released and distributed according to the machine's design. A utensil or container blocking that area can produce a poor wash even with a suitable product.
Understanding this situation
The exact dispenser arrangement varies, so follow the model's loading guide. A tablet found partly intact should be considered with programme choice and position, not treated immediately as a failed pump.
A useful next step
Check the area before starting and use the product as instructed. If the same issue persists on suitable loads and programmes, record where the tablet remains. Do not use an improvised open-door test during washing.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.