Hi Sebastien, thank you for your response!
I've attached the log file obtained via:

journalctl -b 0 > ~/1883292-journalctl-b.log

> that's a process from the gdm user, when did you enter that command exactly? in your user session unlocked? 

Yes, the session was unlocked and my dock station was disconnected.

I haven't restarted Gnome session since I reported the issue; that's what I'm currently getting with dock *connected*:

$ systemd-inhibit --list --mode=block
WHO   UID  USER  PID     COMM            WHAT                                                     WHY                                                         MODE 
gdm   123  gdm   1977595 gsd-power       handle-lid-switch                                        External monitor attached or configuration changed recently block
gdm   123  gdm   1977593 gsd-media-keys  handle-power-key:handle-suspend-key:handle-hibernate-key GNOME handling keypresses                                   block
abram 1000 abram 779132  gsd-power       handle-lid-switch                                        External monitor attached or configuration changed recently block
abram 1000 abram 779130  gsd-media-keys  handle-power-key:handle-suspend-key:handle-hibernate-key GNOME handling keypresses                                   block
abram 1000 abram 778915  gnome-session-b shutdown:sleep                                           user session inhibited                                      block

5 inhibitors listed.


I've just disconnected the dock, waited for a few seconds before laptop screen lights up and ran the same command again; now there are only 3 inhibitors:

$ systemd-inhibit --list --mode=block
WHO   UID  USER  PID     COMM           WHAT                                                     WHY                                                         MODE 
gdm   123  gdm   1977595 gsd-power      handle-lid-switch                                        External monitor attached or configuration changed recently block
gdm   123  gdm   1977593 gsd-media-keys handle-power-key:handle-suspend-key:handle-hibernate-key GNOME handling keypresses                                   block
abram 1000 abram 779130  gsd-media-keys handle-power-key:handle-suspend-key:handle-hibernate-key GNOME handling keypresses                                   block

3 inhibitors listed.

As you can see, the remaining one is the same 1977595 PID as before.

> did you enter that command exactly? in your user session unlocked? it's weird that there is a greeter process around, they should be stopped once the user is logged in

Hmm, I have a different issue which I didn't report yet which I thought isn't related. Sometimes when I connect the dock OR change one of displays settings (like orientation) via Gnome UI the laptop screen goes black. Displays settings UI still shows it as available and I can move mouse, windows etc where it's supposed to be but it's not showing anything. I found that switching to greeter via ctrl+alt+f1 (or f2?) and then back to Gnome session (ctrl+alt+f1/2) fixes this. I believe this is happening since 19.04; I never reported it since I thought it could be one of intel GPU driver bugs and it would be fixed elsewhere.

Now I think this could be related somehow; probably I've faced the black screen issue when I connected the dock, "fixed" it by switching to greeter and then back to user session and this could cause a sleep issue?..

Sorry if my explanation looks confusing; let me know if there's something else I could check.