The coordinate system of the ArcMap map is the coordinate system of the first loaded data by default. When loading other data, the coordinate system will be automatically converted to the coordinate system of the first data.

The loading order of the two data is different. In fact, the coordinate system of the map is inconsistent. The coordinate system of the first map is WGS-84-UTM-zone-50N; the second time is Xi'an 80-3-degree-GK.

-zone-34.

I have not been exposed to your situation. The reason for the huge difference you mentioned is probably caused by the mutual conversion of coordinate systems.