It may concern the support or fitted arrangement rather than only the appliance's glass. Both the installation and hob condition may need assessment.
What the observation means
Do not lift the hob to inspect the cutout or fill a gap with sealant. Heat, loading and recent work provide relevant context without proving a cause.
A useful next step
Stop use where stability or damage is uncertain. Describe the crack's location and any recent fitting changes. Keep building or worktop repairs separate from an ordinary appliance component quote so the correct people can assess the whole arrangement.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.