They are running a bit cold.. try no less than 20c at night and 25c + during the day. I would bet the medium where the roots are is getting too cold.
Is this an average intake temperature or canopy? You'd be surprised how important temperature control is.
With LEDS people want you running hotter than normal too, alot of people run 26c +being the best but try not to swing your temps more than 5c , and keep them hotter
It's tough to control my tents temps like that in the winter it would be too damn hot in my house
The very red stem has me believing that it is temperature but it could be something else too