Randy, are any of your stations passive?
I say this because I've noticed that my passive station with the stock shield tends to run lower in humidity (~2-3%) than my aspirated station (both VP2s with SHT31s). By the way, my FARS unit uses the same Mechatronics fan as yours I believe (UF80B12-BTH).
Could the sensor (and the firmware which lacks averaging capabilities) have been designed for passively ventilated enclosures? It seems forcing air onto it causes it to go a bit haywire with rapidly fluctuating dew points. I noticed this behavior previously with my solar powered stock fan too.
Take yesterday for example. Almost calm winds all day. The dew point from the FARS was a roller coaster varying 6F between the highs and lows (a complete cycle took as little as 5 minutes).
However, with a stronger, steadier wind (5-15 mph), as exists today, the DP smooths out considerably (<1F variations in same time period). This mimics the behavior of a passive enclosure. And the DPs between the two shields converge (1-2F diff with active still higher) under windier conditions.
Both mornings have been clear and sunny with temps in the upper 60s to lower 70s.
Perhaps humidity and DPs need to have a rolling average applied (last 10 readings?) before comparisons can be made on calmer days?