I am presently converting some workshops from 4.14-4.15 to version 4.17. In the Window|level panel, the “Summon World Composition” button brings out an almost blank window:
I found the problem.
In the world composition window version 4.17, the graphics of the layer seems to have a Z of 0.0 (???), like the HUD of the window. But the graphics are at the beginning of the scene drawing so the HUD is hidden (except for the text).
If you zoom out enough with the mouse scroll wheel, you’ll get this window or one similar: