That is a question that is best addressed to O2.
In the last 9 days since release, the AUC8 update has been rolled out to over 100 countries and carriers worldwide, from Afghanistan to Vietnam.
In the U.K. the non carrier branded, stock Samsung version, CSC code BTU, was available on the 29th March. This was closely followed by the carrier branded firmwares for EE, (CSC code EVR), Vodafone, (CSC code VOD), and Three, (CSC code H3G).
For O2 carrier branded phones purchased from O2, (CSC code O2U), they, like the other carrier branded phones, have to certify the update before Samsung can release it. It may be that O2 has requested that changes be made or are simply tardy in their certification process.
No one will have the carrier branded firmware for O2 as it has not been released yet I am afraid.
There will be users on the generic, non carrier branded, phones, (CSC code BTU), that have O2 SIM cards installed that have AUC8 but that will not be the same as the O2 carrier firmware.
Ah, yes! The good old carrier blame game. Very popular with the various U.S. carriers and now, over here in the U.K.
My advice is to wait for the O2 AUC8 update which is is a big 1.1GB download and almost replaces the previous firmware and contains a whole host of fixes and tweaks it would appear.
In the meantime, if you have not already tried it, you should reset your network settings...
Settings > General management > Reset > Reset network settings > Reset settings
... to see if this fixes your issue.