[Fern]

It happens in the test server as well. I've gone ahead and recorded the bug in action. It has made me get stuck consistently with the following encounter:
makemegetstuckgroup.sav
 
Video recording below. If you want to try it on yourself in the test server, just use the encounter I mentioned.

 
It also consistently makes other players get stuck. I've actually not seen it properly start the encounter in the test server at all - it's always making someone get stuck instead.
 
Note: The video recording doesn't show the windows that pop-up when you're selecting encounters and stuff for some reason...