I can reproduce #860839

[Pietro Battiston <me@pietrobattiston.it>]

Dear Debian Qt maintainers,

I just wanted to mention that I was getting exactly the same symptoms
Harlan reported in
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=860839 , and I solved
by running:

sudo ln -sf /usr/lib/x86_64-linux-gnu/qt5/plugins/platforms/ /usr/bin/

as suggested here:
https://askubuntu.com/questions/308128/failed-to-load-platform-plugin-x
cb-while-launching-qt5-app-on-linux-without/522278

I'm reasonably sure my problem originated from some partial upgrade
(I'm using pinning), but that the QT lib packages all come from the
Debian archives.

Cheers,

Pietro