If you are using the XML Editor in Inkscape and your buttons are faded/missing like this
https://www.mediafire.com/convkey/ff07/wy6mlk4sbqgh0216g.jpg
This is the workaround
Known workarounds (0.91, lp:inkscape/0.92.x):
a) close and reopen XML Editor in the current session
b) check ‘Pre-render named icons’ in ‘Edit > Preferences > System’ and relaunch inkscape