Repro for https://github.com/dbus2/zbus/issues/765

Cargo.toml

[package]
name = "gnome-shell-dbus-debug"
version = "0.1.0"
edition = "2021"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[dependencies]
async-std = { version = "1.12.0", features = ["attributes"] }
zbus = "4.2.0"

client.js

const Gio = imports.gi.Gio;
const GLib = imports.gi.GLib;

const iface = `
<node>
  <interface name="net.hadess.PowerProfiles">
    <property name="ActiveProfile" type="s" access="readwrite"/>
  </interface>
</node>`;

const proxyWrapper = Gio.DBusProxy.makeProxyWrapper(iface);

let proxy = new proxyWrapper(
    Gio.DBus.system,
    "net.hadess.PowerProfiles",
    "/net/hadess/PowerProfiles"
);

proxy.connect('g-properties-changed', (changed_properties, invalidated_properties) => {
  log("Properties changed, getting active profile:");
  log(changed_properties, invalidated_properties);
  log(proxy.ActiveProfile);
});

log("Pre set:", proxy.ActiveProfile);
proxy.ActiveProfile = "client-provided-value";
log("Post set:", proxy.ActiveProfile);

let loop = new GLib.MainLoop(null, false);
loop.run();

main.rs

use std::future::pending;

use zbus::{connection, interface, Result};

struct Handler {
    value: String,
}

#[interface(name = "net.hadess.PowerProfiles")]
impl Handler {
    #[zbus(property)]
    async fn active_profile(&self) -> String {
        println!("Getting {}", self.value);
        self.value.clone()
    }

    #[zbus(property)]
    async fn set_active_profile(&mut self, value: String) {
        println!("Setting to {}", value);
        self.value = value.clone()
    }
}

#[async_std::main]
async fn main() -> Result<()> {
    let handler = Handler {
        value: "initial-value".to_string()
    };

    let _conn = connection::Builder::system()?
        .name("net.hadess.PowerProfiles")?
        .serve_at("/net/hadess/PowerProfiles", handler)?
        .build()
        .await?;

    Ok(pending::<()>().await)
}

Stop & disable power-profiles-daemon: systemctl disable --now power-profiles-daemon

craigcabrey@gamerboi:/var/home/craigcabrey/gnome-shell-dbus-debug/scripts$ gjs client.js 
Gjs-Message: 17:28:05.502: JS LOG: Pre set: initial-value
Gjs-Message: 17:28:05.505: JS LOG: Post set: client-provided-value
Gjs-Message: 17:28:05.507: JS LOG: Properties changed, getting active profile:
Gjs-Message: 17:28:05.508: JS LOG: [object instance wrapper GIName:Gio.DBusProxy jsobj@0x2b7abd67cce0 native@0x55bf6a903650] [object variant of type "a{sv}"]
Gjs-Message: 17:28:05.508: JS LOG: null

thanks. I can reproduce the issue too.

Stop & disable power-profiles-daemon: systemctl disable --now power-profiles-daemon

Actually, you can just switch both service and client code to use the session bus instead and then you don't have to do anything special.