A weird behavior in SwiftUI when using a GeometryReader in a ZStack

Badge.swift

import SwiftUI

struct Badge<V: View>: ViewModifier {
    
    let badge: V
    
    func body(content: Content) -> some View {
        ZStack {
            content
            GeometryReader { [self] geometry in
                self.badge
                    .clipShape(Circle())
                    .offset(x: geometry.size.width / 2, y: geometry.size.height / -4)
            }
        }.fixedSize()
    }
    
}

extension View {
    
    func speakableBadge1(diameter: CGFloat, color: Color) -> some View {
        self.modifier(Badge(badge:
            Image(systemName: "radiowaves.right")
                .font(Font.system(size: diameter * 0.875))
                .frame(width: diameter, height: diameter)
                .background(Color.blue.opacity(0.7))
        ))
    }
    
}

extension View {
    
    private func speakableBadge(diameter: CGFloat, color: Color) -> some View {
        Image(systemName: "radiowaves.right")
            .font(Font.system(size: diameter * 0.875))
            .frame(width: diameter, height: diameter)
            .background(Color.blue.opacity(0.7))
    }
    
    func speakableBadge2(diameter: CGFloat, color: Color) -> some View {
        self.modifier(Badge(badge:
            speakableBadge(diameter: diameter, color: color)
        ))
    }
    
}

struct Badge_Previews: PreviewProvider {
    static var previews: some View {
        Group {
            Text("Hello, World")
                .font(Font.system(size: 48))
                .speakableBadge1(diameter: 32, color: .blue)
            Text("Hello, World")
                .font(Font.system(size: 48))
                .speakableBadge2(diameter: 32, color: .blue)
        }.previewLayout(.fixed(width: 320, height: 320))
    }
}