Display manager SDDM doesn't make use of 3rd monitor

I have computer with 2 videocards and 3 monitors attached - 2 to one card and 1 to another one. I run Ubuntu Server with X and I want to use most lightweight display manager as possible. I’m trying to use SDDM but I faced a problem that after boot my system has desktop using only 2 monitors attached to one card and the 3rd monitor is unavailable to it.

I’ve installed and run LightDM with absolutely the same system configuration and after boot with this manager my system has desktop utilizing all 3 monitors.

Is it possible to configure SDDM to work with 3 monitors in my case or this is limitation of SDDM by design?

Here is some information on system running SDDM and LightDM:

1. Xrandr –listproviders are absolutely the same:

Providers: number : 2
Provider 0: id: 0x55 cap: 0x9, Source Output, Sink Offload crtcs: 4 outputs: 2 associated providers: 1 name:Unknown AMD Radeon GPU @ pci:0000:08:00.0
Provider 1: id: 0x93 cap: 0x6, Sink Output, Source Offload crtcs: 4 outputs: 3 associated providers: 1 name:modesetting

2. Xrandr –query has one difference in DVI-D-1-2 section:

LightDM

Screen 0: minimum 320 x 200, current 2293 x 3240, maximum 16384 x 16384
HDMI-A-0 connected 1920x1080+373+2160 (normal left inverted right x axis y axis) 477mm x 268mm
   1920x1080     59.93*+
…
DVI-D-0 connected primary 1920x1080+0+1080 (normal left inverted right x axis y axis) 477mm x 268mm
   1920x1080     59.93*+
…
DVI-D-1-2 connected 1920x1080+143+0 (normal left inverted right x axis y axis) 598mm x 336mm
   1920x1080     60.00*+  59.96    50.00    59.94    59.93  
…
HDMI-1-2 disconnected (normal left inverted right x axis y axis)
VGA-1-1 disconnected (normal left inverted right x axis y axis)
…

SDDM

Screen 0: minimum 320 x 200, current 2293 x 3240, maximum 16384 x 16384
HDMI-A-0 connected 1920x1080+373+2160 (normal left inverted right x axis y axis) 477mm x 268mm
   1920x1080     59.93*+
…
DVI-D-0 connected primary 1920x1080+0+1080 (normal left inverted right x axis y axis) 477mm x 268mm
   1920x1080     59.93*+
…
DVI-D-1-2 connected (normal left inverted right x axis y axis)
   1920x1080     60.00 +  59.96    50.00    59.94    59.93  
…
HDMI-1-2 disconnected (normal left inverted right x axis y axis)
VGA-1-1 disconnected (normal left inverted right x axis y axis)
…

3. Xrandr –listmonitors differs correspondingly:

LightDM

0: +*DVI-D-0 1920/477x1080/268+0+1080  DVI-D-0
 1: +HDMI-A-0 1920/477x1080/268+373+2160  HDMI-A-0
 2: +DVI-D-1-2 1920/598x1080/336+143+0  DVI-D-1-2

SDDM

0: +*DVI-D-0 1920/477x1080/268+0+1080  DVI-D-0
 1: +HDMI-A-0 1920/477x1080/268+373+2160  HDMI-A-0

4. Inxi -Gx shows some fail for SDDM:

LightDM

Graphics:  Device-1: NVIDIA GK208B [GeForce GT 710] vendor: Gigabyte driver: nouveau v: kernel bus ID: 01:00.0 
           Device-2: AMD Raven Ridge [Radeon Vega Series / Radeon Vega Mobile Series] driver: amdgpu v: kernel bus ID: 08:00.0 
           Display: x11 server: X.Org 1.20.13 driver: amdgpu,ati,modesetting unloaded: fbdev,vesa 
           resolution: 1920x1080~60Hz, 1920x1080~60Hz, 1920x1080~60Hz 
           OpenGL: renderer: AMD RAVEN (DRM 3.35.0 5.4.0-91-generic LLVM 11.0.0) v: 4.6 Mesa 20.2.6 direct render: Yes 

SDDM

Graphics:  Device-1: NVIDIA GK208B [GeForce GT 710] vendor: Gigabyte driver: nouveau v: kernel bus ID: 01:00.0 
           Device-2: AMD Raven Ridge [Radeon Vega Series / Radeon Vega Mobile Series] driver: amdgpu v: kernel bus ID: 08:00.0 
           Display: x11 server: X.Org 1.20.13 driver: amdgpu,modesetting FAILED: ati unloaded: fbdev,vesa 
           resolution: 1920x1080~60Hz, 1920x1080~60Hz 
           OpenGL: renderer: AMD RAVEN (DRM 3.35.0 5.4.0-91-generic LLVM 11.0.0) v: 4.6 Mesa 20.2.6 direct render: Yes 

System info:

uname -a
hostname 5.4.0-91-generic #102-Ubuntu SMP Fri Nov 5 16:31:28 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux

lsb_release -a
Description:    Ubuntu 20.04.2 LTS

UPDATE

Just to remove potential problem upgraded using sudo apt update and sudo apt upgrade with no effect.