Some models have an automatic-lock preference. Releasing the lock for one session may not change that standing setting.
What the observation means
A recurring lock symbol can therefore be different from a control fault. The owner menu may distinguish automatic and one-time locking.
A useful next step
Use the exact manual's procedure to review the preference. Do not try random service-menu combinations. If the displayed lock cannot be released through the documented method, record the model and message. A lock does not remove residual heat or replace supervision around a recently used hob.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.