I've been noticing this too. At first what caught my eye was failures in Movable Type, which led me to think there was something wrong with that app (I just upgraded to 3.32).
But then I noticed that if I shell in, start up vi and walk away, when I come back vi has been "Killed", presumably by an admin or an automated process.
This leads me to wonder if DH isn't just killing processes that are long-running (like MT rebuilds) to free up server resources... I hope not, as the threshold seems to be so low as to make the service unusable.