I seem to have the exact same problem as @rosievers , I got sick of my lack of knowledge wiith light dm to get the lock screen to work so I switched from lightdm to gdm.
On initial install all 4 buttons are present as usual.
When I click lock, nothing happens.
When I use super + l, the lockscreen comes up for a millisecond and then the screen goes blank (I wish it would just stay on the blank screen for a short while).
When I log back in from the lock screen, the power button is gone as is the hibernate button. All that is left is the unresponsive lock button and the settings button.
When I lock the screen again (super + l), and then log back in, all that is left is the settings button.
For completeness sake, if I do it again I still have the settings button.
In Tweaktools > Extensions, the “Status menu buttons” extension does have an “error loading extension”, with the button greyed out so I can’t turn it off and I can’t seem to remove it. The error is also present on extensions.gnome.org/local/. However uninstalling from here does not actually work.
I don’t mind moving back to lightdm, as long as there are clear instructions on how to get the lock screen to work, However this is beside the point gdm should not do this.
I have also tried the above recommended instructions but to no avail, only resetting will bring back the power button.
I’m also a noob at gnome so I don’t know how to get to all the settings. I really like the gnome desktop but not having a simple thing like the lockscreen work is very annoying.
Any help would be appreciated.