Nested ForEach + ScrollView Header causes Glitches - swiftui

Question

Inside of a Scrollview I use a LazyVStack with a pinned header, and based on the scroll position I manipulate the scale of that header.
In the LazyVStack, I have a ForEach iterating over some list of items. However, if I use a nested ForEach loop (to have, say, items grouped together by month), the scrollview becomes extremely glitchy/jumpy.
Minimum reproducible code:
struct Nested: View {
#State var yValueAtMinScale: Double = 100 // y value at which header is at minimum scale (used for linear interpolation)
#State var headerScale = 1.0
var restingScrollYValue = 240.0 // y value of scroll notifier when scrollview is at top
var body: some View {
ZStack {
ScrollView {
LazyVStack(pinnedViews: [.sectionHeaders]) {
Section(
header:
Circle()
.fill(Color.red)
.frame(width: 150, height: 150)
.scaleEffect(CGFloat(headerScale), anchor: .top)
.zIndex(-1)
) {
// scroll position notifier
// i set the header's scale based on this view's global y-coordinate
GeometryReader { geo -> AnyView in
let frame = geo.frame(in: .global)
print("miny", frame.minY)
DispatchQueue.main.async {
self.headerScale = calculateHeaderScale(frameY: frame.minY)
}
return AnyView(Rectangle()) // hack
}
.frame(height: 0) // zero height hack
ForEach(1...10, id: \.self) { j in
Section {
Text("\(j)")
// works without nested loop
ForEach(1...3, id: \.self) { i in
Rectangle()
.frame(height: 50)
.padding(.horizontal)
.id(UUID())
}
}
}
}
}
}
}
}
// interpolates some linear value bounded between 0.75 and 1.5x, based on the scroll value
func calculateHeaderScale(frameY: CGFloat) -> Double {
let minScale = 0.75
let linearValue = (1-minScale) * (Double(frameY) - yValueAtMinScale) / (restingScrollYValue - yValueAtMinScale) + minScale
return max( 0.75, min(1.5, linearValue) )
}
}
Removing the inner nested ForEach loop removes the problem. What could be going on here? I figured updating the header scale on every scroll update would be too many view updates and cause glitches, but that doesn't explain why it works with one ForEach loop.