Not sure what is going on, been searching, anyone else have this issue or know what is up?
The inner part of the new leaves are yellow.
Soil amended with mushroom compost, fertilizer alternately with TTF and Masterblend.

https://www.hazera.us.com/deficiency-sy ... oes-crops/

Maybe iron deficiency? Link has several diagnostic looks of various nutritional deficiencies.

I’ve had this with cool wet soils, think it is a deficiency related to the cool wet soil. When things warm up its gone away. I can’t say for sure that’s what you’ve got—is your soil cool and maybe fairly wet?

Your don't have your location in your signature we don't know where you are growing and your weather conditions. Given that, it could be from cool temps. It looks to me like the beginnings of iron deficiency.

What is the pH of your soil? Alkaline or Acidic?

It looks like glyphosate damage, to me. What I've done that has been effective in saving the plant is removing all the leaves with yellow on them (just keep doing that whenever new ones grow). It takes a while, and delays the harvest, but my Cosmic Eclipse plant lived when I did that.

It could be iron-deficiency, though; they look a lot the same.

It could be roundup damage but if it is, it either is very early and/or very minor. I’ve usually had some odd leaf curl with that damage. OP—has it gotten worse or stayed largely the same?

My first thought was 'wet soil' as well. Cold and wet tends to cause nutrient deficiencies. Could be pH related deficiency, alternatively.
But I'm not familiar with herbicide damage.

Here is an article about iron uptake - it may be that your soil is too alkaline.
"In soils that are aerobic or of higher pH, Fe is readily oxidized, and is predominately in the form of insoluble ferric oxides. At lower pH, the ferric Fe is freed from the oxide, and becomes more available for uptake by roots."
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2764373/