That looks like an un heated greenhouse, they probably got cold. Also if you are growing in growbags, did you add drainage holes to the bag? Most people growing in those add a collar to increase the depth of soil the plant is in ( even now you could add one by cutting up a plant pot, wrapping it around the plant and adding compost. Burying some of the stem will encourage more root and make a stronger plant) Hope this helps.
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Hope this helps.