[tsac]

Is you phone a company phone? does anyone have access to your email accounts?
If no to these then it may be the HIB is being used wrong. You can delete massages and phone calls from the HUB and generally one at a time unless you use "select more" action..

Also it ay be the sync is causing this. it is possible the sync direction will delete stuff.
Make sure your clear on the sync your using , direction and where.

If this is a company phone, it is possible for the admin to delete info "wipe" data.

The other thing may be an App causing this. Try deleting any you added then wait for a few days and see if it helps. If it does add them back one at a time and work for a while to see if the problem comes back. If one causes this you have your answer.