Can't find much about this anywhere, and what we have found hasn't worked. There was a post here about deleting the OST file on the PC, and that had no effect. Here's the story.
Starting last week (3/9/2011 or so), a number of people have had significant numbers of their contacts deleted nightly from Exchange/Outlook. We thought it was an Activesync issue, but it also happens to people that do NOT sync to a mobile device (but they do have an A/S device for mail and calendar.
So that seems to tie it down to the Exchange side. The Exchange mail server is 2007 SP 1 RU 9 (a bit behind, but we've been on that level for months with no issues).
So, nothing has changed on the Exchange side. On the Windows side (all Win 7 Enterprise), most of them loaded last weeks patches, and we've deleted them on a couple of PCs to test. We are still exploring that, but it doesn't seem to have fixed the problem.
I would have thought if this was a patch issue, this would be widely known. I can't find any reference to this sort of issue anywhere, except for years ago, for some random iPhone issues. (Again, it doesn't look like a mobile issue, since we have non A/S Contacts users with the same exact problem.)
Are there any nightly Exchange processes that would erroneously delete contacts? Note that it is never deleting all of them, just a good part of them (usually more than half), usually older ones, but not always, usually ones that have duplicated, but not always. No real pattern.
I've been restoring the contacts daily for people, and then they are gone the next day after the overnight whatever processing. So, something actively is processing overnight to do this.