Hello, without a doubt temperature problems, you should be between 22-26 degrees Celsius at most, above 28 degrees Celsius these problems start to appear. I also notice that your watering is very little at this stage of the plant. Even worse if you have excessive temperature issues, I don't know the size of your pot, but I'm at the same stage as you in vegetation in 16L smart pots and I'm watering with 350ml per plant every other day. My temperatures vary between 25-26 degrees Celsius and up to 29 degrees at most.