According to the Bluetooth standard, the range is up to 50 metres - but that only applies in open space with a clear line of sight and no obstacles. In a typical home, the effective range is considerably shorter.
Walls, ceilings, metal shelves, and other electronic devices can weaken the signal significantly. Thermal insulation glass - such as balcony doors - can also interfere with the connection. Sensors that have a direct line of sight to the Hub generally have the most stable connection.
If a sensor is syncing irregularly or not at all, it's worth checking the distance to the Hub and moving the sensor closer. You can also use multiple Hubs - there's no limit to the number you can add in the app, and sensors automatically connect to the nearest one.