Well I have some interesting results.
I purchased two identical wi-fi adapters based on Realtek 5370 chipset.
I attached one of these to my Odroid C2 and low and behold it worked. I could see SSID's of various networks and I could join them! All was well.
Then, I powered down the unit and replaced the wi-fi adapter with the second unit I purchased. On power up I could se the SSID's but I was back to the same problem. Cannot connect to the network.
I had a separate SD card with Armbian on it that had not been run before and so I booted this up with the second wi-fi adapter connected and it functioned fine. Allowing me to connect to any network I could see in the list of SSID's.
I then powered the system down, replace the wi-fi card with the first unit that worked fine previously and guess what? It no longer works. Could see the SSID's but cannot join the network.
So interestingly it appears that once the 5370 based wifi adapter is detected, if you replace it with an identical unit, it stops working. I can only assume it has somthing to do with mac addresses etc. I do notice that when the system works. wlan0 is defined, otherwise it is defined as something completely different (excuse the lack of info here as i do not have the unit running at the moment)
Can anybody suggest a way of deleting referneces to the previous wi-fi card so that I do not have to make separate builds for each device?. I intend on making around 10-15 Odroid based units.