It's not a nutrient issue, I tested the pH and EC.

I also doubt it's dehydration or suffocation, because it's in an optimal hydroponic environment.

So, there's only three options left I guess.

Option 1: wind damage.
It was quite stormy about one or two weeks ago. Maybe it got root damage (unlikely, small plant), or it bend too much?

Option 2: temperature fluctuations.
At the same time of the storm, the night temperatures dropped quite a bit (lowest: 12°C). And now, it raised to 40°C just a few days after.
Or,

Option 3: sunburn.
It's under a shaded cloth, and gets direct sun only at afternoon, if at all.
All other plants (e.g. pepino) do very well and have no light stress.

Or is it something different?

It also lost a few pollinated buds. Is that a very bad sign?

New growth this week has appeared wrinkled as well.