Comment # 3 on bug 1099752 from Wolfgang Bauer

This is basically the same as bug#1099589, it's a regression in Qt 5.11.1.

Should be fixed in the next Tumbleweed snapshot, the offending change has been
reverted:
https://api.opensuse.org/request/show/619726

To avoid the problem, just use the "Quit" option in the menu (or the keyboard
shortcut) instead of closing the window to quit Qt creator.

(In reply to Mykola Krachkovsky from comment #2)
> Almost same here. After removing/renaming of
> ~/.config/QtProject/QtCreator.ini it's back but after a while it hides again.

You actually don't have to delete the config file to get them back.
You can also just re-enable the corresponding views in the menu Window->Views.