Android Devices Fail to WIFI Connect on Airports using Bridge Mode

My configuration:

(1) Zywall USG 100 router providing DHCP for the LAN connected by wire to:

(2) 4 Airport Extremes with static IP in Bridge Mode providing wired and wireless connections WIFI 2.4 & 5 GHz network without Security. DHCP from Zywall provides all IPs unless devices have static.

Problem:

Found airports have to run firmware 7.4.2 (not current versions such as 7.6.1) for Android devices (running version 4.0.4) to connect to the WIFI network. With newer firmware versions on the airports (have the problem), Android devices try to connect and then loop (retry) on the connection while the Airport logs show the Android devices "Associated with station ..." and then "Disassociated with station ...". I have tried all sorts of configurations, static IPs and more, restores and reboots without success (other than rolling back the Airports to 7.4.2). As a side note, I have found certain apple devices also have had difficulty connecting to Airports with newer firmware when using this configuration.

I think the problem is in the Airports and has to do with running some combination of many Airports in bridge mode, DHCP and Androids. Bet other WIFI devices will also have the problem.

Love to hear if any other solutions...