This problem occurs due to the presence of Cisco bug ID CSCsb42280.
When RADIUS is configured for Authentication, Authorization, and Accounting (AAA) for IPSec remote access users, some important RADIUS attributes are sometimes missing in the START and STOP Accounting-Request and Access-Request.
In the START Accounting-Requests, this attribute is missing:
RADIUS: NAS-Port-Id 
In the STOP Accounting-Requests, these attributes are missing: