Datum Transformation cannot be found

[AdelmoCos1]

I upgraded ArcGIS Pro from 10.8 to 10.8.1. When opening existing layout  created from ArcGIS Pro 10.8, the message below pop up every time I open up any layout created from older version.  

I tried to fix the issue but the second transformation shown below cannot be edited.

Any suggestion to fix the issue would be greatly appreciated. 

[TI]

This issue appears to have disappeared with version 3.x (not sure which version exactly).  It is not present in version 3.3 (for me), and was not present in version 3.2.  I can't remember for sure about 3.0 or 3.1.

[Jeff-Reinhart]

Here is a fun twist. When an Imagery Layer in Portal is added directly to a map in Pro, it does not trigger the transformation warning. When the same Imagery Layer is added to a Web Map in Portal and the Web Map is opened in Pro, this triggers the transformation warning. The Imagery Layer references a mosaic.

[Jeff-Reinhart]

Found the issue for our case. Our source raster was in UTM. Then referenced in a mosaic projected to Web Mercator. Then the mosaic was published and added to a Web Map in Portal. Changing the mosaic so it used the source raster UTM projection resulted in the "transformation warning" dialog no longer appearing.