It means the R seats have not been released. CO releases and disables R inventory frequently. Best way to check for R inventory is to start a booking process on the same flights and check the box for mileage upgrade and see if R is available. You need to do this after 5-6pm, as R might be available in the day - then disabled in the evening for the EUA run. If the mileage upgrade is available just before say 9-10pm, then some upgrades will clear.

Say 2 seats in R inventory - then top 2 Plat fares categories get the upgrade. You need to monitor the seat map and see Elite coach seats vacate as then are moved to F. You can tell if others got the EUA and you did not if folks are moved up front. Check the seatmaps again at say 11pm EST to see the upgrade.