Please visit User Meta >> Settings (Login Tab) then choose user login by “Username” and save your changes.
If you still have the issue please provide us following answer.
1. Are you using user-meta-advanced plugin?
2. Are you using user_meta_default_login_form filter hook?
3. Does the issue exist on previous versions than 1.2.1?
Your first suggestion fixed it. None of the options were selected in the login settings by default. Selecting any of the options fixed the missing label. Probably good to set Username as the default. Thanks very much!