Just started today, my license stopped working and noticed I was logged out in Unity Hub.
When I try to sign in it appears to accept my username/password, the window closes, but when I look again it still shows the option to sign in and I am not logged in. No error messages.
I have tried clearing the App Data/Unity Hub and tried uninstalling and reinstalling unity hub.
Got a workaround. Disable your Internet and go through the manual activation process. The Unity hub will create a .alf file for you. Reenable Internet. Go to Unity - Activation and upload the file, and that will give you a license file to download. Download it. Disconnect Internet again and relaunch Unity. Go manual activation, and give it the license file you just downloaded. Quit Unity. Turn Internet back on again, and launch Unity. Worked for me.
Trying to download purchased assets from the store within the editor does not work as well.
Demands that you log into your account, go ahead and enter username/password, nothing at all; still logged out.
You can track the current status of Unity’s services here, seems they’re having a partial outage that is affecting logging into the editor: https://status.cloud.unity3d.com/