I assigned unique SSID's to the 2.4Ghz and 5Ghz networks and my AC devices connected to the 5Ghz fine and I noticed better performance etc.
However after a while, that network drops and my AC devices need to join the 2.4Ghz network (e.g when I try to rejoin the 5Ghz network it just keeps trying but can't connect).
Sorry, I emailed my screenshots of the setup from home to work but the email didn't get through, but I noticed some messages in System relating to the 5Ghz band entering Power Saving mode as it detected no devices on that network were active (this would have being after my devices have been inactive and entered power saving mode).
I have upgraded my Fritz!Box OS from 6.20 to 6.30 (the latest available) in accordance with the troubleshooting info on the Fritz!Box website and it still has the same result.
If I restart the Fritz!Box I can then connect to the 5Ghz network again.
Has anyone else experienced this?