Statistics Sensor random unknown state

I have made a couple of statistics sensors which combined calculate an Air Quality Index.
For this calculation I use 1hr average values of different sensors such as Co2, tvoc and pm2.5.

But I encounter a strange problem with only 2 sensors namely the tvoc average sensors.

Sometimes these sensors report the state unknown without a apparent cause.
De source sensor is reporting values even when the statistics sensor shows unknown.

As you can see there are random interrupts in the data, why… i don’t know.
The following image is from the source sensor:

this is what my configuration looks like:

Is there something i can check in the logs ore something, or does somebody have the same kinda problems, please let me know.

regards,
jordy kleian

Did you ever figure this out? I’m having the same issue today with averaging a humidity sensor.