I've had this same issue when changing the APs IP. Just stops responding. Here's what I did and started working every time:
*Factory reset the AP by holding down the reset button for 15 seconds (ZoneFlex APs need to be powered on).
*Plug into your ZD and wait for it to be added.
*Do not add it to the VLAN yet...
*Open a command prompt and do a continuous "ping x.x.x.x (your IP) -t" You'll get lots of responses.
*Open another command prompt and continously ping the IP you want it to be.
*Change the IP. You'll see the first window stop responding, and then in a minute the second one will. You won't see the AP in the ZD for a few minutes. But you know it's there because the ping is successful. Just be patient. Sometimes it takes 5 minutes or so for it to show up in the console. https://appsync.biz/dafont/ , https://downloader.vip/mapquest/ , https://appsync.biz/filehippo/*If you're going to put it on a VLAN, after it shows up in the ZD you can add it to the VLAN for connectivity.