I am also having this issue. For me only internal calls have link to recording file in the CDR although outgoing calls are still recorded (in the folder).
The link was working a few module-updates ago … I thought it coincided with a change on the extensions module where recordings selections are now “Force|Yes|Don’t Care|No|Never” and used to be “Always|Don’t Care|Never”
I might need a bit of help navigating the asteriskcdr database as per the above suggestion
Seems like an old post has solution involving re-write of call.monitor module
http://community.freepbx.org/t/cdr-source-column-empty-on-reports-and-call-monitor
FreePBX distro version 6.12.65-22
asterisk 13.0.1