Notifications depend on the appliance, network, account and phone settings. A silent phone does not establish that no temperature or power event occurred.
What the observation tells you
A disconnected router can remove alerts during the same interruption affecting the appliance. Battery-saving or notification settings may also delay delivery. Local alarms and appropriate routine checks still matter, within the model's intended use.
A useful next step
Set up monitoring according to the manufacturer's guidance and understand its limits. If an event is suspected, examine the actual compartment conditions and records instead of treating the absence of a message as proof of safety.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.