Also look for RF issues (in my case 2.4 is disabled and 5ghz@40mhz@15dBm only).
1. Check for DFS events (but in case of a radar even your ssid will turn fully off.
# show ap arm history {ap-name <ap-name>}|{bssid <bssid>}|{ip-addr <ip-addr>}
2. Check the user-table, if the user is in the user-table your 802.11 association and authentication are succeeded
# show user-table
3. Show info about the user connection
# show user mac ##:##:##:##:##:##
What does it tell, what AP, what radio and channel, what user-role, what SNR.
4. check if the client roams correctly
# show ap client trail-info
5. check also the errorlog
# show log errorlog
6. Do a packet-capture form the datapath for a client.
# packet-capture destination interface|ip|local
# packet-capture datapath mac 11:11:11:11:11:11 decrypted