The Dabinett I planted this spring are sensitive to something I sprayed in my orchard last week (that would be about August 6th). It was a spray of 0.5% neem, 8% effective microbes, 0.75% seaweed. None of the other varieties were negatively affected. I saw the same problem early in the spring and attributed it to transplant shock. Now, seeing the same issue months later, it's clear it was from the spray.
My guess is that the phytotoxicity stems from the effective microbe treatment. I have sprayed neem and seaweed at the above rate several times with no ill effects but I have not sprayed effective microbes at that rate since the spring.
The effective microbe treatment was made with 2 gallons of starter, 2 gallons of molasses and about 40 gallons of water. Of course, it might be the combined impact of all three at once. Haven't had the chance to be scientific about this.
Varieties that were unaffected by the treatment: Bedan, Stoke Red, Domaines, Ashmeads Kernel, Muscadet de Dieppe, Golden Russet, Harrison, Hewes Virginia Crab.

Nat Bouman
Growing cider varieties in Zone 5b
On B.118 at 18X24
Susquehanna County, Pennsylvania

The foliar rate for effective microbes is 1 to 2 gallons per 100 per acre, resulting in a tank concentration of 1 to 2 percent. The ground rate (used for Spring1 and Fall apps) is 4 gallons per 100 per acre, upping the concentration to 4 percent. If it's even fitting to talk about microbes this way, as the "life density" of the activation process could readily vary based on how each one of us goes about the brewing process. Still, I can't quite see how photosynthetic bacteria, lactic acid bacteria, and yeasts cause phytotoxic symptoms. Especially at this point in the summer, when leaf tissue for the most part has toughened up.

I concur that this is not likely "neem burn" either as you have the foliage rate right for neem oil at 0.5 percent concentration. Sometimes my borer trunk spray made at 1 percent neem concentration hits a lower branch; still, no spotting results. Again, that tough leaf factor past midsummer. Another thread concerning pear sensitivity speaks to earlier-in-the-season damage to tender pear leaves caused by "safe" fatty acid concentrations at 0.5 percent. But you're clear about Dabinett not showing damage earlier. Hmmm.

Lost Nation Orchard
Zone 4b in New Hampshire

We had this happen after a spray where I added just a tad more neem to the tank mix and ALL Dabinett and chisel jersey showed leaf damage the next day. Oops. I did not make a note on which spray this was, but it was more summer than spring. I've apologized to the trees and promise to be more careful this year!

Vista Ridge Orchard
Zone 8a in Washington
235 Cider and heritage apple trees, 72 varieties,

Aha! I noticed this on the Dabinett, Chisel, and Harry Masters Jersey last season. I dropped the neem down and didn’t see any damage from that point on. I’m fairly new to this so I have to say I was a little relieved to see this post.

Lesley Run Orchard, Zone 5b/6a, West Alexandria, Ohio