A proving mode has a specific temperature and moisture arrangement. The wrong programme, unsuitable covering or an unusually long period can change the dough before it rises as intended.
What the observation means
Dough proving is different from keeping cooked food warm. Some ovens add moisture; others simply provide gentle warmth. A recipe written for a bowl at room temperature may need different handling in the appliance. A dry skin on the dough is therefore a useful observation about conditions, rather than immediate proof that the thermostat has failed.
A useful next step
Compare the recipe and the model's proving instructions, including whether the container should be covered. Do not put a bowl of water into the oven unless the manual allows that arrangement. If the appliance becomes markedly hotter than its intended proving behaviour, stop the programme and report the setting and display. Avoid experimenting with successive batches to test an oven that appears to overheat.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.