Visible water level is not a reliable measure of how well every washer is filling. Some programmes use a relatively small amount that sits below much of the door glass.
Understanding this situation
Judge the situation against the model's normal behaviour, programme progress and washing result. A machine that completes normally with properly wetted laundry is different from one that displays a supply warning or leaves a largely dry load.
A useful next step
Do not add buckets of water to compensate for an assumed low level. Report the actual change, any warning and selected programme. Manual intervention can obscure the original symptom and introduce an unsuitable water quantity.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.