I would keep the users place. The user will return to the application expecting it to be where they left it rather than having had it move arbitrarily up. You should notify them that more things have happened but keep the viewport focused on the last place they left it.
this the way facebook do it with their activity stream on mobile, it keeps it's position but a link 'new stories' appears at the top of the page and clicking scrolls to the top.
With an error stream I think this is also very important. If a user sees an error, then looks elsewhere as they are dealing with it, such as online for a solution, at documentation or at a software interface, I think it would be more beneficial to have their place kept. They will want to see the details of the error they are working on not the newest error, unless they choose to look.
It's also worth remembering that moving the screen automatically leaves the user having to find their last place. In an error stream, where there could be 10s or 100s, many with very similar identifying strings and difficult to sum up with an image, finding your last place could be very frustrating, even if you highlight the one they were on, what happens if they accidentally highlight another while scrolling?
Effectively, with a facebook-like solution, you leave the user in control of their viewport, not the system.