Hi Paul,
Sorry to hear you're having issues. My first thought regarding the infinity software no longer connecting is that you still have the atik air app pointing at your raspberry pi. Can you check the AtikAir app and make sure you have it set to 'local'.
With regards to the Raspberry Pi zero. I've only ever tried it on a raspberry pi 3, so am unsure if it'll work on that device. The atik air image for the raspberry pi makes use of the wifi built into the raspberry pi 3 and so, without knowing much about the raspberry pi zero, it's difficult to say what the problem might be. However, if it's recognizing the pi, then there should be hope. Can you get it to connect to devices when the raspberry pi is connect to an ethernet cable?
Chris