This may seem odd, but I read somewhere that dconf and gsettings are two different things actually, they store their settings in different places, so you may want to edit the dconf using the dconf dump and then dconf load.
Maybe it works.
The only other thing that may have already been mentioned is the where gnome actually stores those options for the session, I am not sure but I think Gnome store the settings in one place and how they were set during the session in a different place, then you have to find those files and delete them to see if they are not overriden the gsettings.
$XDG_CONFIG_HOME/config/autostart $XDG_CONFIG_DIRS/config/autostart /usr/share/gnome/autostart
The applications defined in those directories will be started on login. gnome-session-properties(1) can be used to easily configure them.
$XDG_CONFIG_HOME/gnome-session/sessions $XDG_CONFIG_DIRS/gnome-session/sessions $XDG_DATA_DIRS/gnome-session/sessions
These directories contain the .session files that can be used with the --session option.
This directory contains the list of applications of the saved session.
man -Hgoogle-chrome gnome-session
$XDG_CONFIG_HOME = $HOME = ~
There is another place I think it is tracker or something that also store info on the position and size of windows and do have a database somewhere.
$ man -wi --wildcard *tracker*
$ man -wi --wildcard *gnome*
ps: for the full list just run the command on your terminal, it was bit long so I just copy/paste the ones I didn't mention and could be relevant.