This bug happens rarely and randomly. An example: I minimized Audacious (a Qt5 app) and let it play Internet radio. After an hour or so, I un-minimized it by clicking its icon on Desktop; then, only an empty and totally transparent window showed up. Minimizing and un-minimizing again didn't have effect.
I have enlightenment 0.23.1-1 from Arch's repository but the same thing happened before, with Arch packages or my own compilations. It also happened in Debian.
EDIT: I have Intel graphic card and the bug happened on two laptops.