Do you have bugs? Or it’s possible mag/potash deficiency. This is why most LST autos to get more than one big bud. Some do also grow dwarf size. What Nutes have you added?
I would try to get the ph down to 6.5. What’s the ppm of the runoff?
Don’t worry about the odd first set of leaf as long as there not browning and falling off most of them are just a genetic deform but the others look great. When was your last watering? Soak them after they dry out and water...
Buy fox farm happy frog from blains farm and fleet, shipping is reasonable. Buy 3 bags and a bag of perlite and mix them all together. The extra left over will allow you to topdress them later on as needed.
I use this one, sensors are getting more readily available for cheaper these days. Just keep the calibration solutions in sealable containers and check them often for accuracy. I haven’t had any issues with this one yet and it’s a very great price.
Search in amazon for: B07H161MPL
I would only add calmag till you see deficiencies or wait till flowering and add P&K. Only add Nutes at 1/4 strength and I’d shoot to stay under 950ppm runoff for now. It’s okay to let them get in the low 600s and then add a little.
Personally I will go into 24/0 after they start to flower and do 18/6 veg. Had great results doing this and controlling RH and temp was much simpler. Plenty of people say doing this promotes 20-25% more yield but I’d say try to do a little research and see what you believe is appropriate...
It’s also interesting topic to look into a period of dark 24-36 hours before harvest. But keep RH lower and watering very minimal a day or two beforehand.