There are several possible explanations for why the blades of your pole hedge trimmer keep stopping while you're trying to use it. The first explanation could be that it's actually a feature of the device. For safety reasons, some pole hedge trimmers feature automatic stopping and shut-off functionality whenever you let go or reduce pressure on a trigger or button. This is done to protect you from any accidents. The blades might also be stopping due to a technical fault or failure, like a broken clutch or damaged gearbox. It might also be caused by damage to the blades or the blades coming into contact with something that is simply too hard for them to cut through, like a thick branch or a rock. The blades can also get clogged up with grass and debris over time, so it's important to look after your trimmer to prevent this.