Although you were assisted by our Chat Support, I did want to share our solution here in the Community as well. This upload experience seemed to be caused from columns in your file. Deleting all columns except your email address column allowed it to upload properly. In cases where this has happened for other users, we would even suggest renaming any custom fields to something other than "Unmatched." Even matching all file headers to existing custom fields is a workaround that works as well.
Frankie P. Community & Social Media Support
Did I answer your question? If so, please mark my post as an "Accepted Solution" by clicking the Accept as Solution button in the bottom right hand corner of this post.
You can post a new message in the Community or find us on Twitter Mon-Fri 8am-8pm ET, Sat 10am-8pm ET, & Sun 10am-6pm ET. We've got real people waiting to help you out. Click below to start a conversation!