Side brush issue

Hello, I’m very happy overall with my x40 ultra.
Although, most of the time the side brush does not work, I have made sure all the settings are correct, reset the robot, deleted and reinstalled the app, cleared the cache, all these things many times. But most of the time the side brush does not work! I have tried to upload videos but this forum will not let me. “Undefined” error appears.  
Please, dreame support get in contact with me.

I'm sorry for the bad experience. The side brush is not working due to the fact that it may need to be repaired, so you will need customer service to help you out. In the app, select Me > Help & feedback > Contact us, and you will be able to contact customer service.

Thank you for your feedback! Currently, a single video upload cannot exceed 50MB. I have shared your request for larger video uploads with the development team. Please feel free to share any additional suggestions about the forum or the product.

Thanks for replying so quickly guys. I will contact customer service.

Mind is doing the exact same thing but in my case it’s never worked. I’ve done all the steps recommended. I have even had a full new arm and motor fitted. Forums are saying it could be the board which is over 150 uk £. This is extremely common and extremely frustrating and I don’t expect to have to repair a unit that costs over 1000 pounds poor design and quality. If this board is not replayed under the E warranty then basically dreame are just a scam company producing pour quality damaged machines and selling at high end market prices