It's not heat stress or bad genetics... you got a problem with your nutes. I've seen this too many times from all sorts of strains.

Bet your growing Hydro - and didn't change your nutes often enough!

They will come back, just make sure you change the nutes, and keep watch on the EC/TDS. 2 maybe 3 weeks tops then change out the nutes.
HydroDynamics Reviewed by HydroDynamics on . One "finger" leaves? OK, I have two different strains going right now (Blueberry, powerplant) and they are 3 days into flower. About the tops of both girls 'round 3-4 inchs don't have normal leaves. Theres just one "Finger" instead of 5. Now these are clones, and they both have leaves with 3 or 5 fingers, but this is like sustained growth of only finger. Is it heat stress? They've been very vigorus and look healthy, there growing great, is it just nothing to trip over? Rating: 5