Just goes to show how reliable any of our “advice” is. 
We’re all just throwing darts at a wall to see what sticks.
And we all have different walls. 
And different darts.
Welcome to life as a human on planet Earth.
Ain’t nobody knows wtf is going on.
But we sure love weed.
Sometimes they can look a little flopy when just watered . They usualy perk up later. Or sometimes look sad when underwatered. Need to find that balance.
Find an empty container the same size as what your plants are in. Every day at lights on, take that empty pot and fill it with the same soil blend as what the plants are sitting in. Take that pot of soil and use it to compare the weight against the pots with plants in them. If they feel close to equal, water that plant. If the empty pot is drastically lighter, skip that plant for that day and check again in 24 hours.
I would recommend doing some reading on the subject of bottom watering. It’s a fantastic method for assuring your soil gets enough water all throughout the container, and will help keep some of the nutrients in your soil rather than stripping them out by top watering til runoff. You’ll need to do some figuring to determine how much each plant needs, but once you do you’re golden. You’ll still need to top water every so often to get the Recharge in to the soil, but that’s no biggie.
You sure hit the nail on the head there mate👍
I have two Big Bud fems that show similar symtoms as yours and it all happened after I topped them, so I go by pot weight and soil dampness 2"down. They look great mid day but droopy morning and night
If you are using a lot of kelp or other sea products, your sodium might be high. It looks just like under/over watering. Just a thought…