64F is low for the ambient temp, depending on the root-zone temps.
In a perfect world for MJ, the soil temp would be at 75F and the above ground plant temps would be the same.
If you lower the above ground temps to 80 and then lower the root-zone to 70, it's the same thing. An average of 75 for both. MJ works this way within reason.
No, you can't take the root zone to 50 and the above ground temps to 100. That's outside the safe zone on both ends. It makes no difference that they would average the needed 75F. The averaging only works in cases where both temps are within the safe zone of 65-90.
With your ambient temps being at 64F it really makes no difference if the area the plants are in measures at 77F at canopy level. Your lights are acting as heaters for you.
Directing the flow from your fans above the plants, so that the grow area temps heat it before it hits your plants is a great idea. Blowing the 64F air right on the plants might lower the canopy area temps below the 77F you're getting.
If the "claw" went away when you raised the ambient temps of the room, then I'd say that was your cure. Part of becoming a seasoned grower involves adapting to the many cause and effect possibilities that you can run into. Temps both below and above ground are very important.
It's temping to try new strains all the time and fun to have a cool selection of weed, but it has a draw-back. You never get a strain where you're completely familiar with it's characteristics during growing.
With new strains, you always have a learning-curve where you have to react to problems for just that strain. If this type of growing is your choice, then keeping notes on exactly what works is very, very important so you don't have to guess later when you grow it again.
Hopefully, simply redirecting the fan air to not hit the plants, but so it is warmed to the 77F temp before hitting the plants will work for you to resolve the "claw".
When you do figure it out, note it for this strain. It may not work with the next strain when you have another whole set of problems.