Table fields in Microsoft Excel (.xls) files added in ArcGIS Pro display nulls if the fields are formatted with certain formulas. However, the same table displays field values in ArcMap.
This issue may occur due to unsupported field types used for formulas in the Microsoft Excel document. The field type specified in the Microsoft Excel table does not determine the field type used in ArcGIS Pro. ArcGIS Pro uses Geospatial Data Abstraction Library (GDAL) drivers and the supporting OGR Vector Formats to read Excel files. When a Microsoft Excel table is added to ArcGIS Pro, GDAL determines the field type used. Formulas that are not supported by the field type in ArcGIS Pro appear as null values in the attribute table.