Office 365 E3. Excel 2016. New Team Site. Logged in as Site collection owner (global admin).
Attempting to create a new list via the SharePoint app "Import from Spreadsheet"
Steps to reproduce:
1) Create a basic spreadsheet with a single worksheet in Excel 2016 with 4 columns, 3 rows of data. Save and exit Excel.
2) Login to SharePoint online team site as site collection owner.
3) Site Contents-->Add an app-->Import Spreadsheet
4) Enter List name, then click "Browse" button to open .xlsx file location
5) Click "Import"
Result: An unexpected error has occurred.