A heavy stone absorbs heat and changes the load inside the cavity. Its use, position and preheating requirements must be compatible with the appliance.
What the observation means
A stone intended for a barbecue or another oven may not suit the available shelf or its weight limits. Leaving it permanently in place can alter later recipes even when it is not being used directly. Do not place it on the cavity floor without explicit permission.
A useful next step
Follow both sets of instructions and note when the stone was introduced. If cooking changed only afterwards, report that detail. Avoid pouring water onto a hot stone or moving heavy hot accessories to perform an improvised temperature test.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.