Landscape Layer Masks can't be imported

Repro Rate: 3/3

This is a live issue that has been tested to occur in //UE5/Release-5.1 at CL 23058290.

This is also confirmed to not be a regression since this issue also occurs in //UE5/Release-5.0 at CL 20979098.

Images showing the issue the customer is seeing is also attached.

Steps:

1. Create a new project.
2. Create a new basic level.
3. Select the floor from the level and delete it.
4. Click on the Select Mode dropdown and select Landscape.
5. Create a Landscape of size 8129x8129.
6. Create and apply a material to the landscape that has one layer to paint with on the landscape using the following steps:
   1. Create a new Material by right clicking on the Content Browser and selecting Material under Create Basic Asset.
   2. Open the new Material.
   3. Create a Constant 3 Vector node and modify it to have a color you want.
   4. Create a Landscape Layer Blend node.
   5. Attach the Constant 3 Vector Node to the Landscape Layer Blend node then attach the Landscape Layer Blend node to the Base Color of the Material node.
   6. Apply the changes and save the Material.
   7. Go back to the main Editor and in the Landscape Details, set the Landscape Material to the newly created Material.
   8. In the Landscape painting mode, click the "+" Create Layer Info button.
7. Create a Greyscale mask *.png with the same 8129x8129 size using Paint, Photoshop, or some other graphics Editor.
   • Alternatively, you may also used the attached Greyscale mask.
8. In the Landscape painting mode, right click on the landscape layer and select "Import from/Export to file".
9.  Expand the "Layers" section and check the box next to the landscape layer so it's settings becomes available.
10. Click on the "..." button and load the greyscale mask and click Import/Ok.

Actual Result: Landscape Layer Mask is not imported.

Expected Result: This should import the landscape layer mask and automatically paint the landscape according to the mask.