I have seen issues with assigned IP at fallback for my APs. When Fallback upon failure is Enabled and for some reason entering fallback, the previously Static IP 192.168.1.7 is changed to something assigned by DHCP (this time as 192.168.1.91) but setting is still configured as Static IP within IP settings. See screenshot below.
It seems like I have to manually revert to my preferred IP as the fallback seems to be permanent. Is this by design? Also, just changing the Static IP won’t change as it is still managed by DHCP, though nothing indicates that. A changed IP in the Static IP field followed by, Save and quickly a reboot seems to regain the desired IP.
This might be related to earlier issues with network devices fallback to DHCP.