Most I link to Navigraph every time I start a flight with WT G3000?
No you should not.
Which version of G3000 do you have?
Are you always cleanly quitting sim via the main menu?
I have the latest and qutting via the main menu, I get the charts from the dropdown list automatic, but I have to connect to Navigraph from G3000 every new flight, I will contact their support.
Yes, the best would be to report this to WT as they have made the actual implementation. Tokens on our end should be valid for a long time.