Never,
Are you still getting leaves with the problem? Old leaves will not get better.
I just did a mini flush on the 2 I have in flower and it seems I am in the same boat as you. pH 6.7 going in and 7.2 coming out so I think this may be a problem caused by too high pH. I think this is the same reason my clones are not making it. Mothers not in optimal health. I will not be using the soil mixture I made up in the future. This is my fault since I mixed the soil myself. I am 75% sure that at least my problem with this is caused by too much manure in the mix screwing everything up. I also checked my ppm. Going in is 160ppm dehumidifier water with the runoff at over 2400. I think the ph issue is causing lockout and the nutes are building up in the soil.
Just my :twocents:
It is odd that the leathery look does not start until there are 3 or 4 new nodes above it that look fine. At least I have somebody else to sort this out with since this does not seem common enough to find using the search function.
I'll check back in a couple days to see if it is getting any better.