Could it be your autosave? I know mine starts if it autosaves - the default max autosave is 5 min, but if your system autosaves and 2 mins after you get your Interactive Render going, you're only going to get 3 min before it autosaves again, issuing another restart.
I have my autosave for 15 min precisely because of this, to avoid the restart 5 minutes after.