Based on your description, the above error occurs after you add additional items to SharePoint online list. The issue could be caused by that there are erroneous values like #N/A, #NA and so on in data columns, or there are duplicates in your data source.
I would recommend that you connect to SharePoint Online list from Power BI Desktop and check if it works as expected. Also you can pull your data to Excel to check if there are any illegal characters/values and duplicates.
Thanks, Lydia Zhang
Community Support Team _ Lydia Zhang If this post helps, then please consider Accept it as the solution to help the other members find it more quickly.