I have a fresh Ubuntu 16.04.3 LTS directly upgraded to 17.10 and I have an annoying behavior: when double clicking on text to select a word or triple clicking to select a paragraph, it doesn't select anything. I haven't tried to select anything before upgrading.
This is the same across applications (Firefox, LibreOffice and Terminal).
I really do not know what to look for.
I'm currently running Gnome 3.26.2, if it helps for diagnostics :)
Yay, great!
The problem was indeed the double-click delay (Activities > Universal Access > Double-click delay) set to zero. No X11 nor Wayland problem.