Sorry for not getting back to this sooner.
Did you ever upgrade JLinked from a previous version? My best guess is that you created a template override for our login/register page, but didn't update that when you upgraded the extension. Can you check your /templates/<YOUR_TEMPLATE>/html/com_jlinked/loginregister directory and see if there are any files in there? If so, try renaming them so that they no longer override our views and then try registering again. If the fields are hidden, that would explain the issue. You'll need to update your template overrides with the changes we made in the latest release.
If that doesn't help, let us know!
Thanks,
Alex