Well we are considering adding an option for that. But we don’t want this feature to be on by default.
To do it now you need to add and option list push 'redirect-gateway def1 to the openvpn server config.
uci add_list openvpn.server_turris.push='redirect-gateway def1' && uci commit
Note that when you hit apply in the OpenVPN tab this setting will be overriden.
Have you tried to restart your client instead of this delayed restart on your router?