Hi - Welcome to JustAnswer, I'm Paddy and I will be your technician.
This is a common issue, the motor can often pulse on & off or stop, this is a measure to protect the motor from overheating when it is made to work harder due to a blockage restricting the airflow.
There can be a build-up debris and the key areas to check for blockages are:
1. The brush head - is there any hair or fibres restricting the brush rotation or airflow
2. Where the brush head connects to the wand/pipe - remove the brush head and look down the connection towards the brush to ensure it is clear
3. Remove the wand/pipe from the dust collection bin - check the inlet to the dust collection bin this area is prone to build up
4. Remove the dust collection bin - check the inlet from the other side (inside the bin)
5. Brush the bin mesh filter inside the dust collection bin
Checking and clearing at these points should resolve your issue.
I have attached an image to help with the instruction - it is a useful guide.
I hope this helps - if you have any questions please do not hesitate to message me.