In the days of W3 Total Cache 0.9.2.8, I used to see a lot of users (for the UpdraftPlus plugin, which I develop) who had their transients vanish. Transients set with a 9-hour expiry were not found when requested 5 minutes later with get_transient().
This problem seemed to go away when 0.9.2.9 was released.
But now, it seems to be back - I'm seeing the same symptoms in users' reports/logs; some minutes after setting a transient that lasts for 9 hours, we attempt to retrieve it with get_transient() and there's nothing there.
I'm wondering if this item in 0.9.2.10 has anything to do with it?
"Improved Object Cache purge policy performance"