This article explains why the cyber message says the microphone is muted when the proctor could actually hear the student.
The "Microphone is muted" alert appears when there is no sound from the student, no equipment noise, and no external factors.
To the right of the alert is the time at which the no sound was detected:
The proctor might not have noticed that there was no sound in a certain second because most of the time there was sound and the proctor heard it.
There is an option to turn off the "Microphone is muted" alert by unchecking this notification in the Dashboard Exam settings:
