Upgrade to newer versions of either the Military Symbol Editor and/or ArcGIS Pro for Intelligence. This is not reproducible in the latest released versions.
解决办法
Close the old project and reopen a new project.
Click on the Edit tab. Select the Military Symbol Editor Toolbar inside the Features section.
In the Select option, click in the box where "Please click to enable add-in" is written to add the data model to the project. Choose Yes.
Application settings open. Keep Military overlay Database as Default.
In Military Symbology Standard, click on the drop-down. Select APP-6(D). Click OK and OK again to add the schema to the database.
Once the layer package is loaded, In search option of Military Symbol Editor.
Search "Tank". Select Vehicle: Tank: Light or any vehicle
Open the Coordinate conversion tool. Click on the Map point tool. Drag the tool on the map and click on the location to provide a point.
Copy the output MGRS coordinate and paste the coordinate in Military Symbol Editor. The coordinates are added successfully.