Going from 4.2.112 to 4.2.205 along with boot image. The AP's have Static IP.
1. Upgraded backup controller.
2. Using WCS template changed the primary and secondary controller for group of AP's. This will move them.
3. Repeated above step till all the 100 AP's moved to backup controller and got the new code.
4. Upgraded the code on the primary.
Using WCS template moved the AP's back to primary.
out of 100 only 5 AP's moved. Remaining AP's lost the IP address and the AP group VLAN.
Had to create the DHCP scopes for each location to bring them on network and add AP group VLAN.
Got to move another 120 AP's. TAC does not what might have caused this.