Duplicate of BUG-000107672: The basemaps are cached and that cache acts like a raster dataset. When users use a lower output image quality setting, ArcGIS Pro requests a lower dots per inch (DPI) than the export, and that results in receiving a lower levels of detail (LOD) of the basemap - which can have different content in the case of basemaps.
解决办法
In the Export window, keep the image quality as Best.