Hello all!
Re: Firmware, telnet and supervisor password, on my VMG8924-B10A (same firmware). I had to downgrade firmware to v15 before I could issue dumpmdm and retrieve details necessary to login to supervisor, debrand (to gain GUI access to TR-069 and TR-064). I could then upgrade to v18 again whilst retaining access (having saved the details to txt file of course!).
Thank you for this most informative forum. It's been a lifesaver for me with the VMG8924-B10A, other modems/routers and BT fttc dlm.