What exactly is your author archive template doing? I wonder if it would be possible to achieve what you’re after without the need for the file at all.
It’s basically a template for individual user profiles. So, when someone searches for a author on the below listed page, they can click on the artists image and then be brought to their page. If there’s a alternative way though that’d be okay. I turned off WP_DEBUG so its not showing right now.
Yeah, the one you see isn’t exactly an error but a notice. Errors stop the page from working. Notice only show up to tell something but it’s not exactly site breaking.
And yes, it is only shown when wp_debug is enabled.