[Fern]

If you spawn a walking monster, there's a good chance that anyone that gets attacked by or walks into it will "freeze" in the sense that their movement and commands become locked. Relogging fixes this.
 
While this is not 100% consistent, you can get it to happen frequently by simply spawning a bunch of walking monsters and having any character run into or get ran into by them.
 
It can also freeze your .slotgm character if you walk into them by accident randomly as well.

[Snake]

It's as if battle fails to start. I was there for that, and I had a party. The (!) sign appeared above, then disappeared. But no combat was initiated.