For some reason the design you shared the first sketch was not constrained, looked correct in your screen shot!
Also I found if you select a plane while setting up a tangent plane its origin does match the document origin. Still would not recommend using the origin created from planes as they are not predictable. Offset planes from the document origin should be OK though.
Screenshot shows unconstrained sketch and the fixed origin after selecting a plane for reference in the tangent plane dialog.

Mark
Mark Hughes
Owner, Hughes Tooling
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