Display issues resuming from standby

New Manjaro user here.

I have found that when I leave the system and come back later, the displays are off and I cannot get back in without powering down my primary display, logging in, and re-enabling the primary display via NVIDIA settings.

Full setup:
Primary display: LG 34GN8560 res 3440x1440 144Hz Position +0+0
Secondary display: LG 27GL850 2560x1440 144Hz Position +3440+0

Everything appears to work as expected on initial install/login (including activities using the GPU e.g. playing a game).
After I leave for long enough for the displays to go to sleep and come back:
Both displays are all black.
There is a mouse pointer but I can move it around the secondary display. I cannot move it to the primary display.

Identified workaround:
1 - Power down the primary display. At this point I get a login screen on the secondary display.
2 - Log in
3 - Power primary display back up.
4 - Go to Plasma display settings. Only secondary display is available there.
5 - Open NVIDIA Settings. From here I can re-enable and re-position the primary display.
6 - The display is also now listed properly in Plasma settings.

I did try reinstalling the Manjaro Xfce edition and the issue did not seem to reoccur there. Reinstalled again with KDE Plasma edition and the issue returns. Greatly prefer the Plasma experience so hoping I can find why this sleep/resume issue is occurring here, but no idea where to go to troubleshoot.

That must be a typo.
Some people sorted things out by renaming ~/.local/share/kscreen to something else, and rebooting the system, but not sure about the standby part if that helps.
What it might help is to create a fixed layout for your screens in Nvidia X Server and append that to /etc/X11/mhwd.d/nvidia.conf so the Section "Screen" has predefined metamodes for the ports where your monitors are connected.
In other cases you can make use either to enable early KMS via /etc/mkinitcpio.conf and add

nvidia nvidia_modeset nvidia_uvm nvidia_drm

into the MODULES line
or (if you are on unstable or testing branch) you can use the kms entry in the HOOKS line, so it will look like

HOOKS=(base udev autodetect modconf kms keyboard keymap block filesystems)

and then run
sudo mkinitcpio -P
then reboot the system.

Some more info i provided here

and here

Nvidia suggests to enable the nvidia-resume service …
systemclt enable --now nvidia-resume.service
but i don’t use it on my end, so not quite sure if only helps in suspend and hibernate scenarios only.