Suspect poor coverage/not enough AP density - If AP transmit power is already at the maximum, you can enable the lower data rates to allow clients to connect from farther away. This has a negative impact on performance, but it can help the customer understand that additional APs might be necessary. https://www.cisco.com/c/en/us/support/docs/wireless/5500-series-wireless- controllers/116057-site-survey-guidelines-wlan-00.html