Hardware acceleration is broken after removing a seemingly irrelevant xrandr command at start up. How to debug?

I have recently obtained a second monitor. Until yesterday, I used to modify the resolution of my original monitor by running the command xrandr --output eDP1 --scale 0.75x0.75 at log-in via a ~/.config/autostart/xrandr.desktop file. Under the advise of a commenter, I removed this command. To the best of my knowledge, my primary monitor's resolution is now set at 1600x900 via the GUI and there is no longer any autostart hackery.

To my complete amazement, this totally broke Firefox's graphics, even on a totally unmodified profile. I managed to fix this by disabling hardware acceleration on Firefox. Today, I have discovered that attempting to make a plot in RStudio crashes the program unless I force it to render via software (i.e. disable hardware acceleration?). I believe that both programs use the same rendering engine.

In conclusion, it appears that removing this xrandr command has broken hardware acceleration on my machine. I have no idea how this is possible. Where do I start to debug it?

System info:

OS: Xubuntu 20.04

inxi -G

Graphics:  Device-1: Intel UHD Graphics 620 driver: i915 v: kernel 
           Display: x11 server: X.Org 1.20.9 driver: intel resolution: 1600x900~60Hz, 1920x1080~60Hz 
           OpenGL: renderer: Mesa DRI Intel UHD Graphics 620 (WHL GT2) v: 4.6 Mesa 20.2.6 

sudo lshw -C display

*-display                 
       description: VGA compatible controller
       product: UHD Graphics 620 (Whiskey Lake)
       vendor: Intel Corporation
       physical id: 2
       bus info: pci@0000:00:02.0
       version: 00
       width: 64 bits
       clock: 33MHz
       capabilities: pciexpress msi pm vga_controller bus_master cap_list rom
       configuration: driver=i915 latency=0
       resources: irq:129 memory:a0000000-a0ffffff memory:90000000-9fffffff ioport:3000(size=64) memory:c0000-dffff

xrandr

Screen 0: minimum 8 x 8, current 3520 x 1190, maximum 32767 x 32767
eDP1 connected primary 1600x900+0+290 (normal left inverted right x axis y axis) 310mm x 170mm
   1920x1080     60.06 +  59.93  
   1680x1050     59.88  
   1600x1024     60.17  
   1400x1050     59.98  
   1600x900      60.00*   59.95    59.82  
   1280x1024     60.02  
   1440x900      59.89  
   1400x900      59.96    59.88  
   1280x960      60.00  
   1368x768      60.00    59.88    59.85  
   1360x768      59.80    59.96  
   1280x800      59.81    59.91  
   1152x864      60.00  
   1280x720      59.86    60.00    59.74  
   1024x768      60.00  
   1024x576      60.00    59.90    59.82  
   960x540       60.00    59.63    59.82  
   800x600       60.32    56.25  
   864x486       60.00    59.92    59.57  
   640x480       59.94  
   720x405       59.51    60.00    58.99  
   640x360       59.84    59.32    60.00  
HDMI1 connected 1920x1080+1600+0 (normal left inverted right x axis y axis) 530mm x 300mm
   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  
VIRTUAL1 disconnected (normal left inverted right x axis y axis)

I would post a relevant strace, but the output for RStudio is too large to paste anywhere and I do not wish to break Firefox again.

To fix an earlier bug, my .profile contains export MESA_LOADER_DRIVER_OVERRIDE=i965.