Comment 10 for bug 1973467

This also affects me, with a dual-monitor - laptop screen + one external monitor - setup (it's harder to tell if it also happens without the second monitor but I can check that if useful.) The second monitor is connected by either HDMI direct or HDMI via a thunderbolt dongle, and it happens in both cases. The only GPU in this laptop is i915, and it's running Ubuntu 22.04.

It's maybe notable that in some but not all cases, I'll return and the mouse pointer is visible on the otherwise black screen.

Also, it's not smooth. If I lock with super-L:
* I get the lock screen
* after a second, the lock screen fades to black, the laptop screen goes blank (maybe DPMS-off, it's hard to tell) and the external monitor reports "no signal" and turns itself off after a short moment
* they remains off for a few seconds
* they then wake up again and show the lock screen
* after some time (20 seconds maybe) the external says "no signal" again and then powers off, laptop screen goes blank
* it wakes up again, back at the lock screen
* it settles on on with the lock screen showing, no change for a few minutes

That's where I stopped, but I suspect that after some time the screen blanker turns the display blank but doesn't power things off. I can get a more precise sequence if it'd be useful. I ran these with both colour profiles and nightlight disabled, though they were previously enabled.

My hypothesis is that the monitor turning off causes some event that causes Gnome to wake it up (in the past I've noticed windows moving from one screen to another, as if it were unplugged, but I haven't seen that recently), and then some other "let's not repeatedly power cycle things" check stops it happening too much. But that's 100% speculation.