Available with Standard or Advanced license.
The default mosaic method is set to Seamline but all values in the seamline order (SORDER) field are invalid.
When you use the Seamline mosaic method, the values within the SORDER field are needed to determine the proper display order. The SORDER field exists, but since the values are not valid, the mosaic dataset will be displayed in the order that they were loaded.
You can use the Build Seamlines tool to re-create the seamlines. Alternatively, you can use a different mosaic method.