As an update on this, we are still actively investigating the issue causing intermittent connectivity in Fallout 76, as well as other Bethesda games, and our forums. We're working to get you back in-game as soon as possible, and apologize for the inconvenience.
In the meantime, please keep an eye on @BethesdaSupport on Twitter for updates, as well as the Bethesda.net Status Portal.
Final update for this evening: The login and connectivity issues are now resolved and you should be able to head back into Fallout 76. We apologize if this put a damper on your adventuring plans this evening, but thanks for sticking with us while we worked to resolve the issue.
If you continue to experience login issues, please send us a ticket via https://help.bethesda.net/.
Thank you!