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No error is expected in the current due to it being a CC. It will integrate, if current is constant it will be a constant value. If it were a ramp you might expect an average value, similar with a pulse.
A common source for a linear error is the trace or solder resistance of the sense resistor. Of course check the tolerance of the resistor used, but also check to see where your traces route; coming from the pads will typically give the best result with a 2 terminal resistor. Using a meter you can often see a voltage difference between the board terminals, sense filter resistors, and sense resistor with a current in the board. There are 4 terminal resistors made so that the sense filter can be connected to the resistor with a low current path, these are less common but can reduce the connection error if used.
You may note the CC has a 1.5% full scale gain error, so if you replace the part there will be some difference, but I would expect the result to be similar. If you have other boards you might compare results and see if the result is dependent on the unit, board or resistor variation. A calibration per board is a good practice, using a low current is usually a relatively low current is suitable since the CC is typically linear over most of the range beginning to curve near the end points.
