It is beginning of some light damage. It probably doesn't nrequire much adjustment, so don't overreact. start with 2 inches higher and see what happens.
As they get a bit further into flower, you may find you can drop that light down 2 inches again and won't have same problem... that stuff is typically slow-moving symptoms. if worse you get symptoms on leaves first... you still might if you don't adjust the light, now.
I had the same thing in a recent diary (either of the 2 recent ones, just click my avatar to see. 2nd or third week of floer the pistils were a bit new and i singed them. took a while to see the repercussions (slow progression). Sometimes it takes weeks to see the negative effect of what we are doing. Good/bad = tougher to diagnose early, but smaller reaction necessary to fix.