Since the last patch there are instances where a character farming afk just doesn't use any skills anymore and as a result just dies.
I don't know what triggers that, but I watched it happen once. The message was "action unavailable" or something along those lines followed by no action from the toon followed by death.
This is a big problem for a mostly afk grinding game and absolutely frustrating.

Deleted by the writer.

This is happening in arena and bots for me.