Unlock dialog is centered "between" 2 monitors

[beelze]

Distribution

Gentoo

Package version

5.6.3

Graphics hardware in use

NVIDIA Corporation GP108 [GeForce GT 1030]

Frequency

Always

Bug description

Unlock dialog is not centered at primary monitor (like lightdm login for instance); instead it is centered "between" 2 monitors.
Both monitors are 2560×1440, no scaling. No errors from cinnamon-screensaver --debug --hold.

Steps to reproduce

Happens always after auto-lock, manual lock or launching from terminal prompt.

Expected behavior

Unlock dialog should be centered at primary monitor

Additional information

No response

[beelze]

upd:
from README:

monitorView.py: This is a widget that gets placed in the stage that provides the backgrounds or screensaver plugin view. There is one per monitor, and they are positioned directly where each monitor is …

it seems on this stage screensaver doesn't detect monitors but just joint screen

[beelze]

upd:
cinnamon-screensaver 5.8.1 same behaviour, no changes.