Leaves are starting to yellow up a bit and taco on...

Indeed, they seem to grow slowly. Just wait to see what happens since you've already fixed a lot of things. This doesn't look like a cal-mag deficiency to me but could be a heat-stress / light-burn sign. I'll be around, keep us up-to-date, and good luck with these babies!

60cm distance from your LED to your plant is ample distance. I also think that 27 Degrees C is fine as I've ran plants in a 30 Degree C environment without any heat stress with good ventilation. What you need to look at is your humidity as 25% is way too low for a plant in veg. It should be around 50-65%. Secondly, I'd put your plants on 18/6 rather than 21/3 as they need a rest. Plants that are on 24/0 are more prone to sicknesses. Try that and see how you go. Don't over water either, let her dry out completely before watering as you can stunt your plant growth. She will recover. Any help needed just drop me a message. Goodluck

Plants of that size and age should not get anywhere near that much light. You want them to work a little for it to produce those large fan leaves and encourage vertical growth

I don't think it's cal msg. pH could do that, but yours looks fine. It's probably heat stress, due to the lights been too close