Netgear WAC104 5GHz Wifi "Not associated"

Hi,

I have small LAN with a Zyxel Armor Z2 and a Netgear R6220 router doing Fast Roaming.
It works great, but I thought I needed some more coverage and decided to chain a Netgear WAC104 to the R6220 for a 3rd access-point since it was basically an R6220 just without the WAN and USB port. - so what could go wrong?

Well ... to my surprise it seems I can't get the 5GHz radio to turn on. I make a wifi device and add it to the bridge for the LAN ports but it just stays on "Not associated" and dmesg just says:

 [1555.120961] br-guest: port 4(wlan1) entered blocking state
[ 1555.131977] br-guest: port 4(wlan1) entered disabled state
[ 1555.143768] device wlan1 entered promiscuous mode
[ 1555.159389] device wlan1 left promiscuous mode
[ 1555.168571] br-guest: port 4(wlan1) entered disabled state

It seems to work if I try with the 2.4Gz radio ... but then ... client devices won't roam to that from the 5GHz network.

Are there any known issues with the WAC104?

/Peter