thanks for the reply but i don't think is the same.
i have deployed quite a few controller for different clients but this is the first time the client is testing it and therefore i don't exactly know what's the bevavoir. however i think this behavior is quite weirld, i thought that all APs should swing over to the other controller when one of them is down. another thing i obvious is that, after 5-10mins when I finally can see the AP 'swing' over, the uptime is reset, meaning that the APs actually got rebooted.
both of the controllers are connected to 2 different core sw (on trunk) with lacp enabled. I don't think there is anything wrong with the switch config.
anyone have idea of what could be the possible cause?