I had a similar problem with 2 plants of mine in veg. They were in a coco medium and I must have given them too much nutes in one of the feedings... so i flushed out the 14L pots with 30L of PH'd water... the next day I re-introduced them to a slightly lower concentration of nutes and they where fine again. Slowly build your nutrients back up to full strength and you should be good to go !!
Do you have a ph and ec pen? If so do you reguarly check your ph ? How consistent are you with your ph and ec levels?
I know that if you start having ph problems, big fluctuations, than you can get deficiencies, lockouts etc.
Which could also be the cause of your problem !!
Also what medium you growing in? How often do you water? What environmental conditions have you got? (lights,ventilation etc)
The more info you can provide will mean that its alot easier to identify what your specific problem is !
Im only a noob so please anyone who see's any wrong or misleading informationg here please let us know, will also help to build my working knowledge on our beloved herb.