Too much Mg will lock-out nutrients, I'd ease-up on the CalMag. <doh> Ever think of trying molasses? (provides the same stuff but cheaper)

Wait till soil is dried-out a tad and see if any roots are still actively growing (white tips) before the flush. A wet rootball falls apart when checking the roots, so let it dry first. Don't tear-up the rootball checking, just take a quick look. Flush and resume nutrients if looking ok. (perhaps 1/2 strength twice a week)

Worse case...roots are damaged and leaves won't recover. Eventually, I'd harvest and re-veg, including trimming the roots and a good flush once in it's new pot.

Sounds like a soil mix similar to mine. I use it for both vegetative and reproductive stages. (vegging and flowering) Any soil you use will take some getting used to.
With a well-rounded organic soil, you'll likely want to transplant into final container a couple of weeks early to help burn-off some nitrogen before flowering stage hits hard. The ladies will stretch for the first couple/few weeks of flower, but will fill-in if given enough time.