Yea bro you gonna have problems....
-Your ppm in resivour seems low for this stage.
-Your humidity is low too low for the stage of flowering your in.
-Your temps too high with lights on.
I don't know about your nutes and weather they need added cal mag to them...
You may have some other issues... that I wouldn't be able the know of from what you wrote.
-root problems
-irrigation problems
-lighting issues
I would defiantly suggest with getting these factors dialed in.
The plants don't look underdeveloped by any means so I'm sure you can turn save them.
BUT... if this problem continues you will sufffer in harvest greatly.
Good luck.