This article covers 2 of the most common reasons for discrepancies between data you see in YouTube and the results in your Supermetrics reports.
YouTube’s API restricts the types of fields you can pull at the same time. For example, if a query pulls video views and splits them by gender, it’ll encounter an incompatible fields error. This happens because views is a video-level metrics, while gender is a user-related metric.
Viewer percentage is a metric that a query can split by gender, for example, because it’s measured on the user level (rather than the video level).
If you’re not using the Channel totals account option, you might encounter discrepancies in your data.
Using any other settings, or combination of settings, will results in fields having multiplied values for each video listed in the results.