Welcome to the forum.
I was having the same issue and my cause was the temperature in my tent.
It was running about 82*_84* and then when I noticed the taco leaves I lowered the temps to 76F-78F and fixed the problem.
You will have more experienced folks on here give you some advice and you can go from there.
You would benefit from no intake fan at the top. Just exhaust fan and vents on bottom opposite open, but not vulnerable to light at night. This will cause a cooling air flow keeping it closer to the environment outside the tent. Which is easier to change.
Ah using a temperature controller. Yeah lowering temperature would give it more exhaust. Since that’s what the system is basing the exhaust speed at. But you don’t want to intake at the top. Heat rises. 2x4x6 doesn’t need intake fan anyway
Thanks Sincitytoker and Budz I made some changes 1.) moved intake fan from left to right side and made it an extra exhaust fan, it’s only 4” and lowered the high temp trigger on the inline duct fan to 78 deg. Budz since feminized auto flowers don’t depend on a light schedule(not photoperiod) I don’t think it matters about the light so much. I think the light may be a little big for the tent , 400 watts, and I’m running it at 50%, 200 + watts. It’s creating a lot of heat in a small space. My concern about the light was mostly cause I went from 18/6 to on 24 , no
off, about 2 weeks into the grow. I don’t think it affected the plant much…I guess I’ll find out…yikes! Thanks again friends.