A crack still requires stop-use assessment even if the cause is unknown. Absence of a remembered dropped object does not make the damage harmless.
What the observation means
Installation stress, cookware events and other factors need professional consideration rather than a remote assumption. The location and timing are useful evidence.
A useful next step
Leave the hob unused and identify the model. Do not run a zone to see whether the crack changes or try to seal it against spills. Describe any recent worktop, fitting or cookware incident accurately without claiming a confirmed cause.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.