Had this happen to me, too. When I chose to attack two thugs, this is all that appeared: 
Viewing post in Old Bug Report Thread
It does. Every time I leave town and try to fight. I tried it on a lone girl, bugged. I tried going out solo, bugged. I tried a random new game, bugged.
And this is version 0.5.8. I did a clean reinstall. I do that for each update.
This is the only thing that appears, and it does so at loading:
SCRIPT ERROR: hidetooltip: Invalid call. Nonexistent function 'get_node' in base 'Nil'.
At: res://globals.gd:1428
Here's a copy of the save, even though it's not just this save: File
I just did a reinstall and went straight into a random game, encounters work fine. I think the problem came when I tried to change and save the Constants. It's the only thing that was different, and the only time this has bugged out on me was this version. The Constants would save and be usable in a game until I exited the game, next time I boot up the game, the Constants reset. So I think that should be the problem.