NuGet API keys should be tied to identity ( username + realm identity), and identity should not include profile attributes such as regular password, user first name, last name, or email.
Nexus 3.x: Change the regular password of a repository manager user account. This will change the NuGet API key as well. This should not happen.
Nexus 2.x does not change the NuGet API key when password or any other account profile data changes.