Most auto's are slow to start, if under enough light which you have plenty they just squat down till about week3 then start going.
But just encase, how much water are you running through on average, and whats the temp like for the mix, and what are you getting ppm wise from some runoff.
Reason i ask is from my mini bucket tester, i noticed with fabric pots if my side vents were too low and i had a high airflow/turn over rate. Like the bucket fan not having a carbon filter to restrict the airflow. It was increasing the evaporation through my media due to the higher airflow and vent placement in regards to the pot. It caused my ppm to increase in media because the water was being evaporated away faster than the plant could knock back the concentration, and that it was cooling the rootzone greater than ambient due to basically being a mini evaporation cooler.
With it being winter here for myself those would be the first places id check if i was thinking i was having an issue. Solution would just be to restrict or reduce the airflow a bit.