Unusual yellowing does anyone have a ideas..plz

As you can see from the pics 4 plants total all the same strain ayahuasca purple from barneys farm all on the same nutes and are all autopots. Weird yellowing started showing up about 10 days ago but only on 2 plants the other 2 are fine temp is all controlled aswel as humidity so I'm happy enough to rule out an environment issue I hope so I'm more so leaning towards a deficiency or rooting problem, I use canna nutes and now they are on atamis bloombastic aswel, I thought it might have been a nitrogen problem but doesn't that usually start to effect lower foliage 1st this has started at the top of both plants and has worked down to the middle of the plants but all bottom growth is still perfe t green any ideas would be great appreciated and thank you in advance the only good sign I can see is that bud size and growth seems to be all the same across the 4 plants so it hasn't halted bud growth so far

They look damn nice either way
Couldn't really tell ya why the yellowing with the 2
Maybe diff phenos?
Have you checked soil pH?
What about ppfd?

Yep soil is at 6.2 and ppfd at the minute is 940, in my own opinion I'm thinking it's a sulfur deficiency. I foliar sprayed the 2 last night with optic foliar overgrow with a touch of added Epsom salt hopefully does the trick, could be different phenos all I know is they are all from the same strain and seed pack but I'm going to start doing clones I think it will take alot of the guess work iut of everything

Looks like you are about 3-4 weeks of flower. I am going to assume you have switched to bloom nutes. Your plants are going through a huge transformation right now; the hungriest that they have ever been and need N. If you look through the posts here you will see that yellowing is a common complaint at this stage.

Is that coco your using?
if it is coco what ec are you using?

I'm 32 days exactly from flip and yep on bloom nutes not for about 1.5 weeks I gave a little extra N to get them through the stretch and then dialed it back slightly, I'm not 100% but fairly positive they are getting enough N added a touch of cal/mag to so I'll watch them closely whatever it is it's not affecting bud production which is great but thank you for the tips hopefully get them back on track and happy again

And no I'm using canna professional plus soil in a 4 pot auto pot system my ec was at 1.7 which was correct for my stage according to there chart to I increased it too 1.9 today incase they really are hungry so I'll know soon enough the environment is all fully controlled and next goes out of sync so I'm lucky there I guess