I have a Aji pancay that looks very similar. In my case, the plants have been in full sun 6-8 hours a day for 2 months, but we had temps of 95 in the shade, 110 in the sun tues-sat and I attribute the leaf curl to that, as it seems like the leaves are dried out on the outer edges. I moved it out of the sun and into the shade and it`s perking up. Zero sunburn, though. I did just buy some Cal/Mag, to see if that might help.
In your case, I think Geeme has it well covered. The plants are definitely quite stressed for some reason. Given that these have been such fast growing, vigorous plants I wonder whether it could be a nutrient issue, such as Calcium deficiency. These plants behave a little more like Tomatoes than Peppers, at least in terms of speed and aggressive growth. It may be that they are just short of some micro-nutrient.
Have a look at this video. It`s showing
extreme Calcium deficiency. A bit of leaf curl and droop like you have could possibly be a slight lack of Calcium, but I`m really not 100% convinced. I`d bet it`s some nutrient issue, though.