USB-C and HDMI not working simultaneously

Question

I have a Lenovo Thnikpad L-480 (i5-8250U) (Ubuntu 18.04) and I am using two other monitors with it, one through the onboard HDMI port and the second using a USB-C to HDMI, USB-C charging and USB-A dongle (PiBOX India USB C to HDMI Adapter Aluminium Type C USB hub 3.1 to HDMI 4K/USB 3.0/USB C 3 in 1 Converter Cable Charging Port Adapter Cable).

When I plug in the hub in the USB-C port{2} which is part of the docking port, both the monitors are recognised and work awesome, but when I try to use the USB-C port{1} which is primarily used for charging (so that I can also use the USB-C charging port of the hub and have less clutter), the only monitor which is recognised is this hub-connected monitor and not the HDMI port{5} connected monitor.

Side view of laptop: (numbers in curly braces alongisde ports denote the port numbered on this link)

Xrandr output shows that USB-C port{1} is labelled as DP-1 and HDMI port{5} is labelled as HDMI-1

So basically DP-1 and HDMI-1 don't output simultaneously.

I have tried to force output throught HDMI-1 when DP-1 is connected and that doesn't work either.

xrandr --addmode HDMI-1 1920x1080
xrandr --output HDMI-1 --mode 1920x1080

My xrandr output when both monitors are working together with my laptop display

USER:~$ xrandr
Screen 0: minimum 320 x 200, current 3840 x 1848, maximum 8192 x 8192
eDP-1 connected primary 1366x768+1237+1080 (normal left inverted right x axis y axis) 309mm x 173mm
 1366x768      60.00*+
 1360x768      59.80    59.96  
 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-1 disconnected (normal left inverted right x axis y axis)
HDMI-1 connected 1920x1080+0+0 (normal left inverted right x axis y axis) 527mm x 296mm
 1920x1080     60.00*+  50.00    59.94  
 1920x1080i    60.00    50.00    59.94  
 1600x900      60.00  
 1280x1024     75.02    60.02  
 1152x864      75.00  
 1280x720      60.00    50.00    59.94  
 1024x768      75.03    60.00  
 800x600       75.00    60.32  
 720x576       50.00  
 720x576i      50.00  
 720x480       60.00    59.94  
 720x480i      60.00    59.94  
 640x480       75.00    60.00    59.94  
 720x400       70.08  
DP-2 connected 1920x1080+1920+0 (normal left inverted right x axis y axis) 598mm x 336mm
 1920x1080     60.00*+  50.00    59.94  
 1920x1080i    60.00    50.00    59.94  
 1680x1050     59.88  
 1600x900      60.00  
 1280x1024     75.02    60.02  
 1280x800      59.91  
 1152x864      75.00  
 1280x720      60.00    50.00    59.94  
 1024x768      75.03    60.00  
 832x624       74.55  
 800x600       75.00    60.32  
 720x576       50.00  
 720x480       60.00    59.94  
 640x480       75.00    60.00    59.94  
 720x400       70.08  
HDMI-2 disconnected (normal left inverted right x axis y axis)

Solution

Your laptop has a graphics device that supports only 3 displays. (Intel UHD 620)

With that xrandr output it is clear that your GPU has enumerated 5 display outputs, but since your GPU can only support 3 screens, some of those outputs must be mutually exclusive.

Output 1: eDP - The built in screen
Output 2: HDMI 1 or DisplayPort 1
Output 3: HDMI 2 or DisplayPort 2

Output 2 and Output 3 are likely using DP++, which means they can be set to output either an HDMI or DisplayPort signal, but not both at the same time.

It seems that Output 2 is physically connected from the GPU to both the charging USB-C port (#1) and the HDMI port (#5). The xrandr output also seems to indicate that your USB-C hub wants to take a DisplayPort signal, so Output 2 cannot push an HDMI signal & DisplayPort signal at the same time. This is why only one port works at a time; But maybe another hub with HDMI Alternate Mode could get both ports to display the same picture.

Output 3 is physically connected to the USB-C docking port so that you can connect a third monitor without causing this issue.
That docking port may also consume Output 2 if you used a hub or docking station with more than one video port on it.