It does look a lot like Sulphur deficiency.
Red stems point often to Mg or P deficiency, but by looking at the leaves, I'd be more inclined to say Sulphur.
Yellowing from the base, the spotting on the leaves, tips hooking down are markers that point me to Sulphur.
Also I'm not quite sure what your potmix nutrient ratios end up looking like.
Too wet soil could also be the reason for the deficiencies.
You got good size pots, but plants are relatively small that if you water them too often,
you could end up with too wet soil.
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