Reset/Ctrl+Z on pre-labeled video scene creates empty region and clicking it crashes the page

**Describe the bug**
When I work with a pre-labeled video task, if I return the scene to its default state using Ctrl+Z or the Reset button, an empty regions/objects appear in the Regions list.

If I click that empty object, the page reloads/becomes white, so I cannot delete it normally with Backspace.

**Steps to reproduce**
1. Open a pre-labeled video task.
2. Change something in the annotation.
3. Press Ctrl+Z until the scene looks reset, or click Reset.
4. An empty object appears (or numerous objects) in the Regions panel.
5. Click on that object.

**Expected behavior**
The annotation should reset cleanly, or the empty object should be removable normally.

**Actual behavior**
An empty region appears, and clicking it causes the page to reload/crash.

**Screenshots**
Screenshot of broken objects and how the page looks after clicking on the broken object

**Environment**
- OS: Win10 Pro
- Label Studio Version 1.21.0

**Additional context**
If required choices are enabled for regions, it is impossible to save the annotation while broken objects are present, because it is not possible to assign those choices to them.