Multi-monitor does not reconfigure when one display turned off

[Allan]

The release is 20.04.
The gnome-session version is 3.36.0-2ubuntu1.

What is expected:
1. When either monitor is turned off, the monitor that is still on becomes the only monitor.
2. The mouse should work.

What happens:
1. When the primary monitor is turned off only, the space is not updated.
2. When the non-primary monitor is turned off only, the mouse is frozen. This is https://bugs.launchpad.net/ubuntu/+source/gnome-session/+bug/1709159

Long version:
I have two identical monitors hooked up on HDMI.
Let's call them #1 and #2, with #1 left of #2. #1 is primary.

Case 1: Turn off #1 (the primary), leaving #2 on:
The display has not been updated to detect the turned off monitor. The mouse can move around on #2, including going to the #1 space even though #1 is turned off.

When #1 is turned back on, everything works fine too.

Case 2: Turn off #2 (the non-primary) leaving #1 on:
The display *has* been updated to detect the turned off monitor. The mouse cannot move at all, even though the cursor is visible on #1.
This is

When #2 is turned back on, there is another display update (another flicker, plus a Pulseaudio notification of new sink detected since the monitor has built-in speakers).

Other notes:
My card is AMD RX480. Another user in https://bugs.launchpad.net/ubuntu/+source/gnome-session/+bug/1709159 is also using AMDGPU.