fstat(1) may be of some assistance, as it can show you open files and the processes that have them open ... but a quick use of Google with "radiusd" or "freeradius" and "lockf" shows
many hits, including "LOCKF=..." in configuration files.
I've never used any RADIUS application, nor do I know anything about freeradius. That stated, your symptom indicates either a configuration/provisioning problem or an application problem.