When you have windows opened in secondary display (not main) and you disconnect that monitor, then other windows like "Lighting" do not appear on main display. Reopening them does not help.

Reproduction steps:
1. Create new project.
2. Move Editor to main display.
3. Create any window like "Lighting"
4. Drag it to secondary display.
5. Disconnect that display.

Expected result: Window will appear on main display
Actual result: Window is "stuck" in secondary display.

Workaround: Restart Unity.

Notes: If you disconnect main display, then windows will be transfered as expected. Reopening windows does not help.

Reproduced on: 5.2.0f3, 5.5.1f1, 5.6.0b5.