What's in your potting mix?

What kind of lighting are you using? And for how many hours daily?

How are you determining when they need watering? Looks like and uptake of nutritients issue from being too wet.

300w full spectrum LED 16/8 schedule

i either water when I start to see them wilting or when I can pick up the cups and they are very light. Most of them need water about once a week.

Iron deficiency can cause chlorosis but usually that's a PH issue which prevents the plants uptake of iron. Also excessive potassium could block uptake of iron and magnesium. Is this the only plant or all plants exhibiting this issue? Maybe the 14:14:14 is too much K.

Out of 60 plants there are probably 5 or 6 that have yellow veins. i have been using the 14-14-14 osmocote for a couple years at the same dosage but I might remove them best as I can from a couple to see if that changes things. I will have to get a pH meter to test my soil but I will do that as well. Thank you for your help.

What's in the potting mix?

Do the cups have drain holes?

What are the prevailing temperatures? Daytime? Night?

Fox farms ocean forest potting mix. plenty of drainage in the cups. Stays about 70-75 F during the day and about 60-65 at night but it rarely drops below about 63

I'm sorry, what type of plant is this? I have a few inklings on what could be some issues to try and correct here

It is a hot pepper

How are the plants now? Did they die? Veinal chlorosis is associated with diseases.

Id say its a nitrogen defiency osmocote is not giving them what they need in terms of food which causes all kinds of other symptoms to show from possible lockout. Start a feeding program with your waterings and see if that helps. This usually shows on your fastest growing plants as well ive noticed