Did you use adaptive mode because you were having the issue with Apple devices? Has it returned for you since then?   This started happening at a few of my networks, causing issues with iPads and iPhones.   I believe I've tried toggling 802.11r (at least on/off, maybe not to adaptive), but regardless, it still happens approximately once per month. Typically all the authentication errors will be on one AP. Rebooting it resolves until it happens again 3-6 weeks later. ... View more