Hello!
I updated to LibreOffice 5.0 the other day and now the icons for the style bar in all of the programs of the suite went away. If I hover over them I can read what they are and once open they operate normally. It seems to be a bug? .
It happens in all of the programs of the suite, i.e., writer, calc.
Same for me and all my friends, who updated to the 5th version. Still no solution, though.
Alternitevly you can install new Breeze icon theme and apply it.
sudo apt-get install libreoffice-style-breeze
To change the icon theme in LibreOffice, go to Tools > Options > LibreOffice > View and set the icon style to Breeze.