OK, rrd4j could be a source of some of this for older data but usually it takes half a day or longer before it starts decimating the data and replacing it with averages. So that doesn’t explain why the recent data is not working as expected.
If you look in events.log can you confirm that the MotionSensor Item is indeed only being set to 1 and 0? If it is only ever going to be a 1 or a 0 why not use a Contact or Switch Item?
So your Item and Chart are using the Item MotionSensor but these logs are for SensorMotion. Have you changed the name or do you perhaps have two similarly named Items and mixed them up?