Well because CLI is awesome? haha
Though seriously, UI has never been a problem with Cisco,
Through I do recommend doing this
1. Use IE(internet exp) considering your AP is quite old, EoS level old, you probably should and also lower down the sec. settings on the browser as well, and disable pop-up blocker
2. technical causes:
A. Your configuration is still lacking/some errors, make sure to verify, most config errors are missing VLANs, guest-mode not enabled or if MBSSID, then well, MBSSID mode, bridge-group ID for MBSSID
B. You power supply device (PoE or power-supply) is not supplying enought power, check through UI(only way as well is throughUI)
AT: Software Tab
CLICK: System Configuration
SEE: System Power Settings
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