Multiple Monitors Won't go to Sleep When Locking Session - Ubuntu 24.04

Question

Hardware:

• CPU: Intel i5-14400
• RAM: 32 GB
• GPU (Integrated): Intel UHD 730
• GPU (PEG): AMD Radeon RX 7600 TX
• Monitors: 2 Lenovo L24 q-10 / 1 Dell P2422H

Software:

• OS: Ubuntu 24.04.1 LTS (fully updated including pro updates)
• DE: GNOME 46
• Display Server: Wayland

Problem:

1. I have 6 Workspaces setup.
2. All monitors are connected via HDMI: The 2 Lenovo's to the PEG GPU and the Dell to the Integrated GPU.
3. I have a terminal window open on a non-primary monitor, on the 3rd Workspace. Every time I unlock the session, the terminal window jups to the primary display on the same workspace.
4. When I lock the session (using Super+L), all monitors go to sleep (DPMS) and immediately wake up and stay on, sometimes with black screen (but no stand-by).
5. I created a new user and tried locking the session - same effect.
6. I used to have an ancient nVidia GT730 worked just fine...

Any pointers welcome, including ways to troubleshoot. It's driving me nuts.

Thanks!