Sophos AP 10 behind RED 50, unified tunnel

Question

Having some issues with an AP10 behind a RED 50 in Unified mode.

RED setup
•Uplink mode: Client
•Operation mode: Standard/unified
•RED interface has been added to "Allowed wireless interfaces"

AP details
•AP has been approved from "Pending access points"
•AP is listed as Active
•A single Wireless network has been attached to the AP

I see the SSID and I can connect to the WiFi but from there on, I am stuck. I can't browse the web. Weirdly my Outlook was able to sync but I can't access any http or https sites.

If I connect to the same SSID in my main office (not behind a RED), I can easily browse the web. So I suspect that clients with an IP from that Interface can access the web.

Anything else I can check or I have forgotten?
Thank you, Matthias

This thread was automatically locked due to age.

mjpmotw · Answer

FINALLY. 
 I tested two different AP 10 with every release and I always failed. The AP behaved erratic, sometimes the WiFi SSID were visible, sometimes not. Suddenly I could connect, a few minutes later I lost connection. The RED 50 was always stable. 
 I took a AP 15 last week, connected it and it behaved as expected: Everything works. 
 Yes, I do blame the AP 10 and I threw both AP 10 away as this issue costed me like 20h.