Steps to repro:
1. Create a new project
2. Right click on an existing tab, and select: Add Tab | Inspector
3. In the menu, select: Game Object | 2D Object | Sprite
4. Select the newly created GameObject.
5. In the newly opened inspector: for the Sprite Renderer component's Sprite field, pick the built-in UI "Knob" sprite.
6. Click Add Component, Polygon Collider 2D.
7. On the Polygon Collider 2D component, click Edit Collider.

Actual result: No node handles appear, the collider cannot be edited.

Reproduced in: 2017.4.27f1, 2018.4.1f1, 2019.1.4f1, 2019.2.0b3, 2019.3.0a3