Sometimes, when using evolution it will fail to obtain the authentication token for gmail. The fix for this is to restart ‘goa-daemon’ using the command (though the path to the goa-daemon varies by distribution)
goa-daemon –replace &https://www.reddit.com/r/gnome/comments/6cvx5p/weird_evolution_authentication_keyring_problem/
Once restarted, restart evolution and it will probably work again. For me, the goa daemon seems to lose track of its tokens after 6-8 hours of use.