I do not think the problem is caused by bound roots. One benefit of fabric pots is some root pruning. The condition you are experiencing looks very similar to one I am contending with. These are purple haze.
I first noticed it 6/20 day 28 on 12/12 light schedule. Taller plant upper left leaves. A few brown spots.
It progressed. One week later on 6/27
They are growing in peat and I am using Jack’s 321. I asked the forum for help and the consensus
was pH lockout. The vessels I am using also complicated matters. I am trying out a sub-irrigation system in 5 gallon buckets. I drained and flushed the reservoir buckets and also flooded the reservoir bucket to try to flush the peat. This was unsuccessful so did a major traditional flush. Garden hose in the driveway on 7/5, day 43
close up of some of worst leaves
This photo is from 7/20 of the most affected plant. It appears the damage has been slowed or stopped for the most part. The damaged leaves will not heal. My hope is to stop further damage and get them to harvest.
The target pH for peat is 6.0. The pH had climbed to 6.5. This initiated the flushing process.
My most recent check the pH has swung the other direction to 5.5+_ and ppm are higher than it should be. Today I will use pH water, no nutrients but add bud candy and nirvana to achieve good runoff.
You said you are in FF ocean forest with runoff ph of 6.5. Normally I would think this is acceptable.
However, the leaves are saying something else. If I was to suggest anything it would be to 6.8 ph water to 20 - 25% runoff. Then water again with calmag at 6.8ph. I am certainly no plant doctor and need help from other growers. Lets see if @Hellraiser
have a minute to look at your plant, what I did to mine, and have a recommendation for you.