A few things to try:
[ul][li] Disable Opus from running at startup. (Preferences - Launching Opus - Startup)
[/li]
[li] If you exit Opus and wait a few seconds, is the smartfav.osv left intact? (Look at the file using Explorer rather than Opus, of course.)
[/li]
[li] If the file is still okay, what happens if you restart Opus after exiting it? Still intact?
[/li]
[li] What if you exit Opus and wait a few seconds, then reboot? Does the file survive the reboot? (As before, check using Explorer to avoid starting Opus.)
[/li]
[li] Enable Opus to run at startup again. Now, if you exit Opus and wait a few seconds, then reboot, does the file survive?[/li][/ul]
That should tell us if it's a problem with Opus shutting down, Opus starting up, Opus being killed during a reboot before it can shut-down, or something to do with user-profile synching etc.