If you are facing issues with keyboard mapping in ubuntu which is the most common error currently you can use the below solution,

Find your start up script

find / -name xstartup

in file xstartup

You have to add the line export XKL_XMODMAP_DISABLE=1 before /etc/X11/Xsession or gnome-session (in case you use GNOME)

export XKL_XMODMAP_DISABLE=1

restart your vnc and all is fixed