Authentication request became stale, challenge sent, no response received from client when connecting a Apple phone using OSX 11 with 802.x. When switching from one NAC to another, the user has to forget network and re-authenticate. It's happening to most Apple phones.
Which AP and Wireless Controller did you use? What is software version? Does this issue happen on windows device or android device also? If not, maybe it is apple phone's issue. Does this issue happen on both radios (2.4Ghz and 5Ghz)?
Kindly request your could collect Real Capture from AP and Open the case to our GTAC.
Sounds like you have different certificates on each NAC. You either need to put the same certificate on both, or provision a wifi profile with a CA for both certificates (which is fairly annoying to do without onboarding software).