Switching the map coordinate system from the default (WGS 1984 Web Mercator (Auxiliary Sphere)) to WGS 1984 GCS and then back to WGS 1984 Web Mercator (Auxiliary Sphere) disables the option of Planar measurement method when using the Measure Distance tool in ArcGIS Pro 3.1.2.

Workaround

Workaround 1

1. If there is data in the map in a different Projected Coordinate System (PCS) (such as state plane), select the coordinate system and then switch back to WKID 3857 (PCS WGS 1984 Web Mercator (Auxiliary Sphere)).
   1. Follow the workflow outlined below:
      1. In the Contents pane, right-click Map.
      2. Click Properties.
      3. Click Coordinate System.
      4. Change the Coordinate System to the data's PCS.
      5. Click OK.
      6. In the Contents pane, right-click Map.
      7. Choose Properties.
      8. Click on Coordinate System.
      9. Change the Coordinate System to WKID 3857 (PCS WGS 1984 Web Mercator (Auxiliary Sphere)).
      10. Click OK.

Workaround 2

• Delete the map with the defect.
• Insert a new map.
  • Optionally, rename the new map.

Steps to Reproduce