I have had several flights with availability in O where an upgrade from C to F using eVouchers did not clear (immediately). Just recently, I talked to LX's CCC regarding availability for an upgrade and, since I hadn't redeemed my eVouchers from Select Benefits yet, the agent instead checked and confirmed the upgrade availability via miles (also saying that the availability was the same as when using eVouchers), but in the end there was no availability via eVouchers (on a flight showing F8 A7).