Power Query Merge causing missing values (~7k difference in totals)

I’m merging two large tables in Power Query, but I’m running into a data accuracy issue.

After the merge, I noticed that the sum of a specific column is about 7,000 less than the total in the original table. So it looks like some data is missing during the merge.

I’m working with large datasets, and I want to properly debug this.

What are the most common reasons for missing values after a merge?

Could this be join (e.g., Inner vs Left)?

How can I identify exactly which rows are missing?

What’s the best way to troubleshoot this and make sure no data is lost in the merge?

Any help or tips would be appreciated 🙏