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Based on the error message, this is a known limitation on the SharePoint side rather than Power BI. SharePoint has a lookup column threshold, and when the number of lookup-type columns (including Person, Managed Metadata, etc.) exceeds that limit, queries can fail with a 500 error like the one you’re seeing.
Because of that, once the new columns were added, Power BI may no longer be able to retrieve data from the library.
From what I’ve seen, there isn’t really a way to bypass this limit directly or exclude those columns at query time from the SharePoint backend. Some possible workarounds you might try:
- Reduce the number of lookup-type columns (if possible)
- Split the data into multiple lists/libraries
- Create a view with fewer lookup columns and connect Power BI to that view instead
- Flatten the data before bringing it into Power BI
Also, I happened to come across this article while troubleshooting a similar issue, it’s not an official Microsoft source, but it explains the limitation and some practical workarounds pretty clearly: How to avoid Lookup Column Threshold limit on a view | SharePoint Maven (just sharing as a reference from another user’s perspective.)
You can also refer to the official documentation for more details on SharePoint limitations: The number of items in this list exceeds the list view threshold - SharePoint | Microsoft Learn
If none of the above helps, you might want to consider opening a support ticket so Microsoft support can take a closer look at your specific setup.
Hope this gives you a bit more direction!