A forum topic on the support forum for the Gutenberg plugin for WordPress states that the undo/restore keyboard command Ctrl+Z (or Cmd+Z on Mac) removes all the previously entered tags. Below is a screencast where this issue is replicated.
Issue: When you add tags to a blog post and remove one tag and continue working by pressing Ctrl+Z or Cmd+Z on your keyboard for the Undo command, all the previously entered tags are removed rather than seeing the deleted tag reappear.
Variations: During the attempt to replicate before recording the screencast the tags were not removed as shown in the screencast. But the tag that was manually removed did not reappear when pressing Cmd+Z, not until I saved the first draft of the post. Then, and only then, the manually removed tags to the post reappeared when I pressed Cmd-Z on my Mac keyboard.
- Core: WordPress 5.0.2
- Plugins: None
- Theme: Twenty Nineteen, Version: 1.1