Comment 9 for bug 1886672

Apologies for the delayed reply. I've done some additional testing, including the Wayland session. Here my findings:

removed .config/monitors.xml and .config/monitors.xml~
unplugged monitor cable, unplugged monitor power
shutdown > start-up
Set display preferences for single/laptop screen
shutdown > start-up
plugged in monitor power
plugged in monitor to laptop
- no change -
opened display settings
monitor starts up as second screen
changed settings as needed for both screens > apply > keep settings
second monitor switches off
shutdown and restart > second monitor on and with correct settings
lock screen > wait for second monitor to go back to sleep
-- correct behaviour resumes --
wake screen > both monitors resume as expected
suspend machine > resume > both monitors resume as expected
-- END--
unplug second monitor > single/laptop display resumes correctly
plug second monitor back in, display remains unchanged (laptop/single only)
unplug second monitor
suspend laptop
plug in second monitor
resume laptop, second monitor remains off
logout
login screen displayed with second screen now enabled
login
display resets to multiple display desktop but second screen remains off
remove second screen > display resets correctly to single laptop screen
shutdown
--- correct behaviour resumes --
plugin in second monitor
start
both screens active including login
login
both screens working as expected
lock screen > all screens suspend
move mouse to active screens > both resume and can login
suspend
suspend machine > resume > both monitors resume as expected
suspend > unplug second monitor > resume > single display/laptop works as expected
-- END --
suspend > plugin in second monitor > resume > display remains in "single" mode > second monitor remains off
restart gnome-shell (Alt+F2 > r) display resets to correct two display setup with second monitor on
lock screen > monitor suspend > move mouse to activate screens > only laptop screen wakes up
shutdown
--- correct behaviour resumes --
start
both screens active including login
login
both screens working as expected
lock screen > all screens suspend
move mouse to active screens > both resume and can login
suspend
suspend machine > resume > both monitors resume as expected
END TESTING

Wayland
---------
setup second display, all working as expected (lock screen and suspend resume work fine)
remove second screen > screen resets to single display
plug in second screen > no change
open display settings > display settings do not recognise second screen
logout
login screen, both displays work
login > both displays working as expected (lock screen and suspend resume work fine)
suspend > remove second display > resume
single display resets as expected
suspend > add second screen > resume
second screen remains off, display remains in 'single' display mode.
logout
login screen, both displays work
login > both displays working as expected (lock screen and suspend resume work fine)
END WAYLAND TESTING

Thanks for the time and effort all.