The base receives heat through the dish and its position in the oven. A wet filling and a different dish material can change that result without a new appliance fault.
What the observation means
A thick ceramic dish behaves differently from a thin metal tin, and a tray placed beneath it adds another layer. The relevant recipe may specify a preheated tray or a particular shelf, but that arrangement must also be allowed by the oven. Placing food directly on the cavity floor is not a general solution.
A useful next step
Compare the recipe's dish and shelf instructions with the arrangement actually used. Record whether the base problem occurs across unrelated dishes or only this wet filling. If the same established method suddenly changes, include the heating mode and cookware details in the repair enquiry.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.