I recently installed Ubuntu 18.04 LTS and my Backspace key isn't working any more in any application.
I think it's unlikely to be a hardware problem because on the same day, before uninstalling a different operating system (non-Ubuntu), it still worked.
When I try adding Backspace to the Keyboard shortcuts, it automatically becomes "disabled".
I'm afraid I currently don't have any other keyboards I can try on my laptop. I have tried resetting the Keyboard under Settings.
$ xinput list
⎡ Virtual core pointer id=2 [master pointer (3)]
⎜ ↳ Virtual core XTEST pointer id=4 [slave pointer (2)]
⎜ ↳ SIGMACHIP Usb Mouse id=9 [slave pointer (2)]
⎜ ↳ ETPS/2 Elantech Touchpad id=13 [slave pointer (2)]
⎣ Virtual core keyboard id=3 [master keyboard (2)]
↳ Virtual core XTEST keyboard id=5 [slave keyboard (3)]
↳ Power Button id=6 [slave keyboard (3)]
↳ Video Bus id=7 [slave keyboard (3)]
↳ Power Button id=8 [slave keyboard (3)]
↳ Lenovo EasyCamera: Lenovo EasyC id=10 [slave keyboard (3)]
↳ Ideapad extra buttons id=11 [slave keyboard (3)]
↳ AT Translated Set 2 keyboard id=12 [slave keyboard (3)]
$ setxkbmap -query
rules: evdev
model: pc105
layout: us,us
variant: ,
KeymapNotify event, serial 24, synthetic NO, window 0x0, keys: 4294967234 0 0 0 16 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 KeyRelease event, serial 25, synthetic NO, window 0x3400001, root 0x13f, subw 0x0, time 500463, (693,296), root:(788,381), state 0x10, keycode 36 (keysym 0xff0d, Return), same_screen YES, " XLookupString gives 1 bytes: (0d) " XFilterEvent returns: False KeymapNotify event, serial 26, synthetic NO, window 0x0, keys: 63 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 KeymapNotify event, serial 26, synthetic NO, window 0x0, keys: 63 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 KeymapNotify event, serial 26, synthetic NO, window 0x0, keys: 63 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 KeymapNotify event, serial 26, synthetic NO, window 0x0, keys: 63 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 KeymapNotify event, serial 26, synthetic NO, window 0x0, keys: 63 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 KeymapNotify event, serial 26, synthetic NO, window 0x0, keys: 63 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 KeymapNotify event, serial 26, synthetic NO, window 0x0, keys: 63 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 KeymapNotify event, serial 26, synthetic NO, window 0x0, keys: 63 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 ClientMessage event, serial 28, synthetic YES, window 0x3400001, message_type 0x136 (WM_PROTOCOLS), format 32, message 0x134 (WM_DELETE_WINDOW)
xev -event keyboard
, focus the appearing application window, press the backspace key a few times, close the application and add its output to your question? Thanks.