Mosaic datasets have their own analyzer. This ensures that the mosaic dataset is functioning properly and efficiently. This mosaic dataset has not been analyzed.
Solution
Use the Analyze Mosaic Dataset geoprocessing tool to analyze the mosaic dataset.
More information
When sharing a mosaic dataset as a web layer, the mosaic dataset will be analyzed. This analysis is at a higher level and will not examine the contents of the mosaic dataset. It is recommended that you analyze a mosaic dataset using the Analyze Mosaic Dataset tool before you share it.