Some suggestions/solutions
1.Consider repotting to allow those roots to stetch a little into clean fresh soil. I have found that this can overcome most issues around PH fluctuation/salts/nutes build up etc in late veg/early flowering. Wont do any harm at all if done carefully and confidently and gives you a chance to take a quick look at those roots! Big pot I know but it can always be done once you get the hang of the best way.
2. Change soil/feed next time! Miracle Grows not the best medium for these plants, workable but not ideal.
3, Be careful if you do flush, it takes a good time for those roots to dry out again and recover. Personally I always choose option 1, even during flowering and with no harm done at all.
4. Nice plant
To recap: repot, feel those roots. Dont feed or water for a few days if the compost is already moist. Cut back on the MG, maybe try another nutrient as suggested above. Give it a week or so to recover before flowering then relax and enjoy it
Hope this helps, but whatever you decide to do, good luck