https://github.com/aevyrie/bevy_mod_picking/issues/117

bevy_chess_picker_bug.rs

use bevy::{
    math::Vec3,
    pbr::{PbrBundle, PointLight, PointLightBundle, StandardMaterial},
    prelude::{
        shape, App, Assets, Color, Commands, Mesh, Msaa, PerspectiveCameraBundle, Plugin, ResMut,
        Transform,
    },
    window::WindowDescriptor,
    DefaultPlugins,
};
use bevy_mod_picking::{
    DebugCursorPickingPlugin, DebugEventsPickingPlugin, DefaultPickingPlugins, PickableBundle,
    PickingCameraBundle,
};

fn setup(
    mut commands: Commands,
    mut meshes: ResMut<Assets<Mesh>>,
    mut materials: ResMut<Assets<StandardMaterial>>,
) {
    commands
        .spawn_bundle(PerspectiveCameraBundle {
            transform: Transform::from_xyz(-6.0, 5.0, 3.5)
                // change z from 3.5 to 3.499 (or less) fixes it
                .looking_at(Vec3::new(4.0, 0.0, 3.5), Vec3::Y),
            ..Default::default()
        })
        .insert_bundle(PickingCameraBundle::default());

    commands.spawn_bundle(PointLightBundle {
        point_light: PointLight {
            intensity: 1500.0,
            shadows_enabled: true,
            ..Default::default()
        },
        transform: Transform::from_translation(Vec3::new(4.0, 8.0, 4.0)),
        ..Default::default()
    });
}

fn create_board(
    mut commands: Commands,
    mut meshes: ResMut<Assets<Mesh>>,
    mut materials: ResMut<Assets<StandardMaterial>>,
) {
    let mesh = meshes.add(Mesh::from(shape::Plane { size: 1. }));
    let white_material = materials.add(Color::rgb(1., 0.9, 0.9).into());
    let black_material = materials.add(Color::rgb(0., 0.1, 0.1).into());

    for i in 0..8 {
        for j in 0..8 {
            commands
                .spawn_bundle(PbrBundle {
                    mesh: mesh.clone(),
                    material: if (i + j + 1) % 2 == 0 {
                        white_material.clone()
                    } else {
                        black_material.clone()
                    },
                    transform: Transform::from_translation(Vec3::new(i as f32, 0., j as f32)),
                    ..Default::default()
                })
                .insert_bundle(PickableBundle::default());
        }
    }
}

pub struct ChessPlugin;

impl Plugin for ChessPlugin {
    fn build(&self, app: &mut App) {
        app.add_startup_system(setup)
            .add_startup_system(create_board);
    }
}

fn main() {
    App::new()
        .insert_resource(Msaa { samples: 4 })
        .insert_resource(WindowDescriptor {
            title: "Chess!".to_string(),
            width: 1400.,
            height: 1000.,
            ..Default::default()
        })
        .add_plugins(DefaultPlugins)
        .add_plugins(DefaultPickingPlugins)
        .add_plugin(DebugCursorPickingPlugin)
        .add_plugin(DebugEventsPickingPlugin)
        .add_plugin(ChessPlugin)
        .run();
}