4.15 on linux on GTX550Ti shows black windows

I’m trying to run UE4Editor 4.15 on linux (Cinnamon desktop) on a GTX550Ti using nvidia-378.13_2 drivers, but any windows opened by it (even notification popups etc) are just black rectangles. buttons still seem to be responding though, as clicking in the upper right corner (where one would expect a close button) exits the editor.

stdout+stderr combined log: paste