After adding bones to a 2D character for skeletal animation, exiting and reloading the program changes the Root Bone to a missing transform and empties the Bones list (on components with the Sprite Skin script attached).

This only happens with PSB files when using the PSD Importer package.

When this happens, you can no longer move or see the character bones in the game scene. If you are using IK Manager 2D it also stops working due to the loss of bones.
The same thing does not happen if you are using a sprite sheet instead of a PSD Imported file.

Repro:
1. Create a new project and import 2D Sprite, 2D Animation and 2D PSD Importer into the project. (Window -> Package Manager)
2. Import in sprite PSB of a character made for skeletal animation.
3. Set Texture Type Sprite, and Sprite Mode to Multiple. Ensure Character Rig is checked.
4. Open Sprite Editor.
5. Change the mode from Sprite Editor to Skinning Editor in the dropdown menu.
6. Click "Create Bone". Add some bones to the character.
7. Click "Auto Geometry" and then "Generate For All Visible".
8. Click "Apply" in the sprite editor.
9. Drag the sprite into the game scene. Move around some of the bones. Note the root bone and bone associations in the Sprite Skin scripts on certain children of this gameobject.
10. Save and exit the unity editor.
11. Open up the unity editor again.

Expected Outcome: The root bone and bone associations should remain on the character in the scene. You should still be able to tweak the character using the bones.
Actual Outcome: The root bone transform is missing and the bones list is empty on objects with the Sprite Skin script attached. You can no longer tweak the character in the scene.

The PSB file of a character for skeletal animation has been attached to this case.

Reproduced in 2019.3.0a11 and 2019.3.0a1
Also Tested in 2018.4.5f and 2019.2.0a11 - no issues in these versions.