Three Monitor Setup with P2419HC + Intel graphics using daisy chain

I'm trying to daisy chain three Dell P2419HC displays to my ThinkPad X1, but the third display doesn't accept the desired resolution of 1920x1080. Setup looks like this:

System

• i7-1165G7, Intel Iris Xe graphics
• Ubuntu 20.04.4, Kernel 5.14.0-1027-oem
• GNOME 3.36.8

Connection (see below for an update)

X1 <--USB-C--> Display 1 (MST On, also has peripherals and USB-to-CAT attached)
<--DP--> Display 2 (MST On)
<--DP--> Display 3 (MST Off)

xrandr

Screen 0: minimum 320 x 200, current 4440 x 1080, maximum 16384 x 16384
eDP-1 connected (normal left inverted right x axis y axis) 1920x1200 60.03 + 59.95 1920x1080 59.93 1600x1200 60.00 1680x1050 59.95 59.88 1600x1024 60.17 1400x1050 59.98 1600x900 59.95 59.82 1280x1024 60.02 1440x900 59.89 1400x900 59.96 59.88 1280x960 60.00 1440x810 59.97 1368x768 59.88 59.85 1360x768 59.80 59.96 1280x800 59.97 59.81 59.91 1152x864 60.00 1280x720 60.00 59.99 59.86 59.74 1024x768 60.04 60.00 960x720 60.00 928x696 60.05 896x672 60.01 1024x576 59.95 59.96 59.90 59.82 960x600 59.93 60.00 960x540 59.96 59.99 59.63 59.82 800x600 60.00 60.32 56.25 840x525 60.01 59.88 864x486 59.92 59.57 800x512 60.17 700x525 59.98 800x450 59.95 59.82 640x512 60.02 720x450 59.89 700x450 59.96 59.88 640x480 60.00 59.94 720x405 59.51 58.99 684x384 59.88 59.85 680x384 59.80 59.96 640x400 59.88 59.98 576x432 60.06 640x360 59.86 59.83 59.84 59.32 512x384 60.00 512x288 60.00 59.92 480x270 59.63 59.82 400x300 60.32 56.34 432x243 59.92 59.57 320x240 60.05 360x202 59.51 59.13 320x180 59.84 59.32
DP-3-8 connected 1920x1080+1920+0 (normal left inverted right x axis y axis) 527mm x 296mm 1920x1080 60.00*+ 1600x900 60.00 1280x1024 75.02 60.02 1152x864 75.00 1024x768 75.03 60.00 800x600 75.00 60.32 640x480 75.00 59.94 720x400 70.08
DP-3-1-8 connected primary 1920x1080+0+0 (normal left inverted right x axis y axis) 527mm x 296mm 1920x1080 60.00*+ 1600x900 60.00 1280x1024 75.02 60.02 1152x864 75.00 1024x768 75.03 60.00 800x600 75.00 60.32 640x480 75.00 59.94 720x400 70.08
DP-3-1-1 connected 600x800+3840+0 left (normal left inverted right x axis y axis) 527mm x 296mm 1920x1080 60.00 + 1600x900 60.00 1280x1024 75.02 60.02 1152x864 75.00 1024x768 75.03 60.00 800x600 75.00* 60.32 640x480 75.00 59.94 720x400 70.08 

As you can see, DP-3-1-1 is connected with 800x600 @ 75.00. Changing it to any higher resolution/rate combination than 800x600@75, I get an error (640x480 or 720x400 do work as well):

CptSnuggles@CptSnugglespc:~$ xrandr --output DP-3-1-1 --mode 1920x1080 -r 60
xrandr: Configure crtc 2 failed

I checked the Dell documentation for correctly chaining the displays and the Intel help pages about my graphics driver if it actually supports my wanted setup. Everything looks possible and correct to me, I don't know what's wrong here. Any ideas? Thanks!

Update: So, I fixed it by attaching two USB-C cables to my laptop.

Connection

X1 <--USB-C--> Display 1 (MST On, also has peripherals and USB-to-CAT attached) <--DP--> Display 2 (MST Off)
X1 <--USB-C--> Display 3 (MST Off)

xrandr

Screen 0: minimum 320 x 200, current 4920 x 1920, maximum 16384 x 16384
eDP-1 connected (normal left inverted right x axis y axis) 1920x1200 60.03 + 59.95 1920x1080 59.93 1600x1200 60.00 1680x1050 59.95 59.88 1600x1024 60.17 1400x1050 59.98 1600x900 59.95 59.82 1280x1024 60.02 1440x900 59.89 1400x900 59.96 59.88 1280x960 60.00 1440x810 59.97 1368x768 59.88 59.85 1360x768 59.80 59.96 1280x800 59.97 59.81 59.91 1152x864 60.00 1280x720 60.00 59.99 59.86 59.74 1024x768 60.04 60.00 960x720 60.00 928x696 60.05 896x672 60.01 1024x576 59.95 59.96 59.90 59.82 960x600 59.93 60.00 960x540 59.96 59.99 59.63 59.82 800x600 60.00 60.32 56.25 840x525 60.01 59.88 864x486 59.92 59.57 800x512 60.17 700x525 59.98 800x450 59.95 59.82 640x512 60.02 720x450 59.89 700x450 59.96 59.88 640x480 60.00 59.94 720x405 59.51 58.99 684x384 59.88 59.85 680x384 59.80 59.96 640x400 59.88 59.98 576x432 60.06 640x360 59.86 59.83 59.84 59.32 512x384 60.00 512x288 60.00 59.92 480x270 59.63 59.82 400x300 60.32 56.34 432x243 59.92 59.57 320x240 60.05 360x202 59.51 59.13 320x180 59.84 59.32
DP-3-8 connected 1920x1080+1920+402 (normal left inverted right x axis y axis) 527mm x 296mm 1920x1080 60.00*+ 1600x900 60.00 1280x1024 75.02 60.02 1152x864 75.00 1024x768 75.03 60.00 800x600 75.00 60.32 640x480 75.00 59.94 720x400 70.08
DP-3-1 connected 1080x1920+3840+0 left (normal left inverted right x axis y axis) 527mm x 296mm 1920x1080 60.00*+ 1600x900 60.00 1280x1024 75.02 60.02 1152x864 75.00 1024x768 75.03 60.00 800x600 75.00 60.32 640x480 75.00 59.94 720x400 70.08
DP-2-8 connected primary 1920x1080+0+402 (normal left inverted right x axis y axis) 527mm x 296mm 1920x1080 60.00*+ 1600x900 60.00 1280x1024 75.02 60.02 1152x864 75.00 1024x768 75.03 60.00 800x600 75.00 60.32 640x480 75.00 59.94 720x400 70.08 

I'm wondering if there is maybe a limitation regarding too many things attached through a single USB-C cable?

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