See my screenshots:
http://steamcommunity.com/sharedfiles/filedetails/?id=135443842
http://steamcommunity.com/sharedfiles/filedetails/?id=135443715
And that's Dutch for "At least I'm making screenshots" for anyone who wonders.
Basically we had some sort of lag spike and now there are no mobs yet the next wave is not coming.
However, there are some invisible barriers around the room which I assume are some remnants of the slimes that used to be there.