I would guess that Brix burn is probably from an environmental factor. In my case, I'd blame it on low humidity. And I was never careful about when I sprayed my Brix, usually around mid-day - wrong time of day.
And so I got burn pretty soon. That also let me see the symptoms - small burned spots resembling a calcium def, and crispy leaf edges. For all we know it IS a calcium def, brought on by getting the leaf metabolism all out of whack with concentrated Brix on a leaf.
But I'm sure that RH at 60% keeps a lot of issues from showing up. And it seems logical that Brix in particular, needs high humidity to work properly. So, spray in the morning when it's cool and dewy, and don't let RH fall below 40%, and you won't see Brix burn.