My mum bought a Viomi V2 pro robot vacuum on my recommendation (I love mine) but it keeps going over the same spot in the hall and appears to fixate on it and will not continue to clean the remainder of the hall. Only stops when you send it to charge back. It is brand new. Could this be a problem with the unit and could be replaced or is this a common problem? There are no obstacles in the hall. The carpet is plush and quite deep, about 10mm. Any advice would be appreciated.