This bug appears only with "GNOME Classic" session.
How to repeat:
1. Install Ubuntu 17.10 2. apt install gnome-shell-extensions 3. reboot 4. login choosing "GNOME Classic" session 5. open terminal 6. do "notify-send foobar" 7. unreadable notification box appears
Thus, I was able to get rid of this problem by choosing "GNOME on Xorg" session.
This bug appears only with "GNOME Classic" session.
How to repeat:
1. Install Ubuntu 17.10 extensions
2. apt install gnome-shell-
3. reboot
4. login choosing "GNOME Classic" session
5. open terminal
6. do "notify-send foobar"
7. unreadable notification box appears
Thus, I was able to get rid of this problem by choosing "GNOME on Xorg" session.