I would say I see at least two things to think about after looking at your pictures. The first thing is your nutrient solution. Not all plants like strong fertilizers. Peppers are one of them.

I am guessing that you have no way to determine how much nutrient your plant is getting other than measuring out the solution? The second thing I see is that likely your PH is high or low, that your plants cannot get a good drink of water.

In order to determine how much nutrients your plants need, the only way I know of is to use a tester/meter. You can buy a dual tester for about $100. Hanna makes a nice water proof one. Once you get a good tester, you need to determine how much nutrient you need to add to the water.

The way this is measured is by PPM (parts per million) or EC (electric conductivity). The most accurate method is by EC, but if the solution is not moving when you test it, the PPM works fine too.

Basically you put the meter in the solution/water, and add solution until the desired PPM or EC is reached. For Peppers at transplant stage, 250 PPM is fine. When a Pepper gets to about 10-12" tall increase to 500 PPM. You can go up to like 1500 PPM on a Pepper, but that is a full grown, heavily laden with fruit plant. Tomatoes can take a high PPM, like almost double of a Pepper.

In regards to PH, PH controls the amount of nutrients and water you plant can absorb. High or Low PH locks out some nutrients, or blocks water from being absorbed. Peppers love a PH of 6.3, while tomatoes I find like 5.8-6.2.

The other thing I would suggest is the flushing of your media with water with a PH 6-7, between every time you drain and replace your nutrient solution. Change out your solution every 5 - 7 days, and never add more solution to a plant after your initial solution setup.

Buy some PH up and PH Down. You use this is small quantities to raise and lower your solution PH without affecting your plant. Test your solution at least once a day and twice if you have time.

Just some things I have learned. Hope it helps.

Thanks for the feedback. I do not have a PPM/EC meter, but I do test and adjust the pH, which has been maintained at about 6.0. I also flush with plain water every week, when I change the nutrient solution.

So maybe the issue is one of nutrient concentration?

Yeah, your problems look like they could be nutrient related, but my question is how frequently do you check the pH? It looks like you might be having some fluctuations that are locking out certain nutrients.