Same with me!
There is also a unusual behaviour, when I try to log into developer.nvidia.com:
The direct login fails (same error message: incorrect email or password).
If I click on “CREATE AN ACCOUNT”, the next page let’s me choose an existing account and then - suddenly - I am logged into the developer space.
If the actual packages like Jetpack 4.2.1 could be downloaded separately, I could use the offline-mode of the sdkmanager. But I don’t find any download link.