I'm having that same issue - thought it was overwatering, but plant has been drying out and it's still like that. All other leaves are fine except for a couple of sets. I am going to increase the sun they get today (there is a shade over my greenhouse because it was very hot a couple of days ago) and see if that helps...if there is more sun today.

My pictures (in plant problems and on my grow journal) show the exact same issue.

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