3rd week into flower phase

I have a strange issue, I've been growing with Ebb and Gro for entire year, this is my 9th crop with this system.

I have one room with 42plants in two gallon pots split up between two 55gallon drum resvoirs, both get the exact same nute mix of GH gro,micro and bloom plus cal/mag and silica. **I alsways add less nutes, never over nutes.

out of 42 plants, most are with very healthy buds forming, the strain is Mendo Purps, I will post a pic later tonight. the leave look great on those ones.

Problem plants: there are about 10 to 12 plants with half healthy buds and the other half look like the picture. Very little hairs and sort of knobby.
***NOTE it's split between the resvoirs, some ill forming buds, so it's not just out of one resivoir.

I am flushing all the plants, for the last 2 days.

Has anyone encountered this issue?
**I just uploaded pics I took tonight of my plants

 

the nutes are always mixed into water in the res, and ph'd

Bump:
anyone using ebb and gro system have this issue?

so,after a week of pure water and flushing, the hairs are growing back on undeveloped flowers.

Added mild nutes monday, things seem to be ok at this point, the grow will need to be extended to make up the additional time spent in flush.