I would say it could be a combination of things that have occurred and are now problems.

Nutrient burn
Nutrient lockout
pH problems
Incorrect temperatures
Incorrect watering
Incorrect application of nutrients
Soil too compact and/or wet
Lack of aeration to the root zone, therefore poor root health.

The damage is permanent and will slowly worsen even if the problems are addressed.
Although it will affect overall yield, hopefully it won't be by a lot.
Try to ensure you gather as much information about your setup then correct the problems. Don't do anything too drastic as it will probably lead to further issues.
Let us know how it goes.