You should better to open a case & pick up some logs.
In another vendor, not ruckus, the reason of the same troubles was:
While SIP call initiation, AP crashes and Kernel panic seen. Root Cause: While SIP call initiation, WLC sends AP_SIP_CAC_CALL_BW_PAYLOAD to AP. The Payload contains SIP INVITE message, which further has to be sent to client. After AP receive the payload, AP makes Packet (SIP INVITE) from buffer inside the payload but didn't set transport header location in the packet. While the packet reach IPClassifier element, Transport header is dereferenced and crash happens. This issue got exposed after IPClassifier element was inserted between sip_snooping_tx and todev_aprXvY path
You'd better open a case in Ruckus.