Radon test spiked only for first hour

I have an RS300 Radon tester that gives hourly results. The home has an existing Radon mitigation system. The test shows a 5.0 pCi/L for first hour, 2.4 second hour and under 1 the rest of the time. I actually ran the test for 3 days. It’s a newer machine so don’t think the calibration is off. Curious if that would be a house issue or a machine issue?

Got my answer. Thanks

In Illinois, not sure of other states, the first 4 hours of data from a continuous monitor may be discarded or incorporated into the result using system correction factors.