I see a few things going on there. I see what appears to be either variegation or mosaic virus. I see the twisting (that is directly related to pH, my answer is to try ranging it up and down, see which the plant prefers. I just did it last Christmas with a gifted poinsettia, so now I *know* the twist is pH). And then I see those necrotic areas.
Finally... the '
cal-mag', a product I have grown to detest. None are at appropriate ratios IMO/E. The vast majority give you a ratio of Ca:Mg at 2:1-3:1, and especially in coir this is quite deficient in Ca. I prefer 4:1 as a base, 6:1 is even better. I find myself wondering if more Ca would be helpful here, despite the fact that the burning you're showing is not classically associated with -Ca IME. Additional Ca may help two issues, the burned/necrotic areas, and the variegation/mosaic. I haven't had much experience with that myself, but I've read many growers who will increase the "
cal-mag" and see the variegation go away. Insufficient Ca is an issue with damn near all other mineral nutrients as well, and since coir locks onto it, I see additional Ca in your regime as a good thing all the way around.
There are a few ways to get more Ca into the plant. When growing in coir my preferred is BioLink Organic 6% Ca. Otherwise gypsum (CaSO4) is a good alternative, it can be top-dressed. Otherwise, find a Ca-only product that you like, and get that ratio as close to 4:1 as you can.
I would also still try ranging pH, even though you're keeping generally within the parameters I've found to be best (my range is 5.8-6.2, generally 6.0 is what almost all strains I've run in coir prefer). I'd let it go as low as 5.6 and expect to see twisting get worse, but frankly I'll be mildly surprised if they like it higher than 6.2.
One last thing--double check your pH meter. If you're using colorimetric drops, double check those. If you're using a meter, make sure it's calibrated and reading properly. If using strips, again, double check your readings against something else.