I have the same issue , all Ap's disconnect the clients for about 4 sec every 10, 15 minutes :
Client (mac='6C:88:14:EC:59:18') has successfully authenticated using 802.11 authentication on interface (value='r2v2') using SSID (value='TV') 2020-05-29 08:49:18,086 AP received a deauthenticate request from client (mac='6C:88:14:EC:59:18') on interface (value='r2v2') using SSID (value='TV'). Reason code: (value='Unspecified'). Total number of clients: (value='0') 2020-05-29 08:49:14,747 AP sent a deauthentication request to client (mac='6C:88:14:EC:59:18') on interface (value='r2v2') using SSID (value='TV') with a reason code (value='Previous authentication no longer valid') 2020-05-29 08:49:14,484
My configuration is a MSM760 (6.6.8.1-23399) Enterprise Licenses, with 5 MSM560 (6.6.8.1-23399)