Sorry for the late reply. I'm on 32bit.
I've recently upgraded to 5.1.0 and still get the same problem if I turn user interface error reporting back on. Additionally, after a period of time I lose the project filing suggestion functionality. I.e. a new email entering my inbox will have no project assigned (even if it's part of a conversation that has been previously assigned). Clicking the project dropdown reveals a completely empty list.
However, if I exit Outlook and restart it springs back to life for a while. If I figure out what it is that's killing the function I'll report it.


