1. You are doing SymbolData.Volume. NOTE: this is the current, at the moment, volume for the day. NOT the volume at the time the candle is processed in the paintbar. For scans, that is usually not relevant since they are always run on the last candle, but in the paintbar it is important.
2. Another reason for discrepancies between paintbar and scan/paintbar could be if their setups are not same. When you run a scan, you specify what candle size you're running it on and the extended hours setting. Make sure they match with the chart on which the paintbar is.