Repro from scratch:
- create a scene
- add a UI>Text element
- anchor it on the *right* side via the rect transform inspector (hold alt to set position)
- resizing the window should move the text element
- after undocking it and resizing it, re-docking it won't move it
- resizing the dock window positions it correctly

Reproduction steps(GIF attached):
1. Open attached Unity project.
2. Open "MIDIUnified > Examples > Sequencer > Scenes > Sequencer" scene.
3. Drag game view window out of the fixed position.
4. Resize it.
5. Put it back into fixed position.
6. UI position and scale doesn't update for the new size.
7. Resize the game view now.
8. UI position restores.

Reproduced with: 5.4.0a5, 5.4.0b10
Not reproducible with: 5.4.0a4