Mac issue extracting ZIP - stuck at LIBAVCODEC

I'm using 10.9, you might need to switch off Gatekeeper.

His osx is 10.11, the latest release and we have already tried with Gatekeeper.
No problem, we'll search for another tester to try the app
Thanks SimonS

We found a new tester with 10.9 and it works perfectly!
At this point it is really an issue of the new OSX El Capitan 10.11.
I read on the internet they have restricted permissions and some apps are no longer compatible or usable.