There was a problem with LibreOffce 5.* used in Gnome 3.20 on an Arch Linux with the 4.4.*-lts kernel. The Display that is used is a HDPI so I am not sure if this is the reason.
Anyways, the problem was that the menu, all the menu entries as well as the font and the content was displayed with four or up to eight the size. If you want to click on something, there was a minimal size lane of size you could go but all in all, it is not a joyful ride.
I could not really find a search term that pointed me to the solution so I tried a lot.
- open the file /etc/gdm/custom.conf
- uncomment the line "WaylandEnable=false"
Hope you will stumble upon this entry and it will solve your problem