I could see all activity in the log just like when I first purchased the modem (before provision) including the CM file downloaded.
I started to think about what others mentioned about what happens when the next update happens (back to square one) as next time I may not get help so I returned the 6120 for the Zoom 5341.
With the Zoom it was the same as with the 6120 in that everything was logged until the modem had a firmware update (right after provision) then the log no longer functioned except critical info.
BUT, with the Zoom it is not an issue as the modem CM file is listed on the status page so it does not matter about updates messing it up.
I am also getting better signal levels with the Zoom.
If you keep the SB6120 and want to see what cm file the modem is acquiring just download and run DHCP Force.