Hi Troy,
as always thanks for the super fast respone :D
it's a hardware CP-HW-5K..
5k capacity with 500 enterprise license installed.
so far i only see Android devices experience the problem. though, the users are mostly android users, only few uses iOS. windows users are excluded from onboarding at the moment.
the client only has onboard tls cert. nothing else.
the uses 3400 series controller with OS version 6.3.0.2.
i will try check the tech-support of the controller later. thanks
R.L.