The KVM switch is a star tech SV211HDUA4K

Here is the log starting from when I switched it.

The computer had one built-in laptop screen, which was disabled at the time I hit the switch, and one external monitor attached to the switch, through HDMI.

I would have expected the laptop screen to be configured as the sole output display, as you would get if you unplugged the HDMI cable.

The laptop screen is 2560x1600 and the monitor is 3840x2160.

[649451.148] (II) event15 - Corsair Corsair Gaming K70 LUX Keyboard  Keyboard: device removed
[649451.176] (II) config/udev: removing device Corsair Corsair Gaming K70 LUX Keyboard  Keyboard
[649451.178] (II) UnloadModule: "libinput"
[649451.178] (II) config/udev: removing device Corsair Corsair Gaming K70 LUX Keyboard  Keyboard
[649451.179] (II) UnloadModule: "libinput"
[649451.264] (II) event18 - Logitech M510: device removed
[649451.424] (II) config/udev: removing device Logitech M510
[649451.425] (II) UnloadModule: "libinput"
[649451.511] (II) modeset(0): Allocate new frame buffer 2560x1600 stride
[649451.512] (II) event19 - Device 2Port KVMSwitcher: device removed
[649451.553] (EE)
[649451.553] (EE) Backtrace:
[649451.553] (EE) 0: /usr/lib/xorg/Xorg (?+0x0) [0x555f7581ef79]
[649451.553] (EE) 1: /lib/x86_64-linux-gnu/libc.so.6 (__sigaction+0x40) [0x7fee2ac5b050]
[649451.553] (EE) 2: /lib/x86_64-linux-gnu/libc.so.6 (__nss_database_lookup+0xd2a) [0x7fee2ad71c4a]
[649451.554] (EE) 3: /usr/lib/xorg/modules/libshadow.so (?+0x0) [0x7fee2a4e0b6e]
[649451.554] (EE) 4: /usr/lib/xorg/modules/libshadow.so (?+0x0) [0x7fee2a4df279]
[649451.554] (EE) 5: /usr/lib/xorg/modules/libshadow.so (?+0x0) [0x7fee2a4df2e4]
[649451.554] (EE) 6: /usr/lib/xorg/modules/drivers/modesetting_drv.so (?+0x0) [0x7fee2aa150b3]
[649451.554] (EE) 7: /usr/lib/xorg/Xorg (?+0x0) [0x555f756b027d]
[649451.554] (EE) 8: /usr/lib/xorg/Xorg (?+0x0) [0x555f758188f3]
[649451.554] (EE) 9: /usr/lib/xorg/Xorg (?+0x0) [0x555f756ab603]
[649451.554] (EE) 10: /usr/lib/xorg/Xorg (?+0x0) [0x555f756af85c]
[649451.554] (EE) 11: /lib/x86_64-linux-gnu/libc.so.6 (__libc_init_first+0x8a) [0x7fee2ac4624a]
[649451.554] (EE) 12: /lib/x86_64-linux-gnu/libc.so.6 (__libc_start_main+0x85) [0x7fee2ac46305]
[649451.554] (EE) 13: /usr/lib/xorg/Xorg (?+0x0) [0x555f75698b71]
[649451.554] (EE)
[649451.554] (EE) Segmentation fault at address 0x7fee11e54000
[649451.554] (EE)
Fatal server error:
[649451.554] (EE) Caught signal 11 (Segmentation fault). Server aborting
[649451.554] (EE)
[649451.554] (EE)
Please consult the The X.Org Foundation support
	 at http://wiki.x.org
 for help.
[649451.554] (EE) Please also check the log file at "/var/log/Xorg.0.log" for additional information.
[649451.554] (EE)
[649451.856] (EE) Server terminated with error (1). Closing log file.