The method described in this post wasn't working for me, and I was still getting auto-upgrades. After some digging, I now believe that if the orbi has already downloaded the new image, it will auto-update even if the NVRAM settings indicate not to auto-update. I did the following to update NVRAM (I found a few more settings that might be problematic?) and delete the update image (text partially copied from original post).
<<start from previous post>>
Perform these step after you downgraded the firmware to a prior release.
1) Launch your favorite web browser and go to <Router IP Address>/debug.htm
2) Login <username> <password> when prompted
3) Check Enable Telnet
4) Start a Telnet session. I use Putty. Enter the <Router IP Address> Telnet is using port 23
<<end from previous post>>
5) Run the following commands:
nvram set upg_status=0
nvram set upgrade_orbi_image=0
nvram set upgrade_base_image=0
nvram set orbi_auto_upgrade=0
nvram set upgrade_check=0
nvram set auto_upgrade_flag=0
nvram set upgrade_satellite_image=0
nvram set orbi_auto_upg=0
nvram set fwupgartriggered=0
nvram set auto_check_for_upgrade=0
nvram set manual_upgrade=0
nvram set auto_update=0
nvram set detect_update=0
nvram set fw_check_tonight=0
nvram set fw_check_status=0
nvram commit
rm /tmp/uhttp-upgrade.img
rm /tmp/have_new_img
9) Type exit to terminate the telnet session
10) Go back to the <Router IP Address>/debug.htm web page and uncheck Enable Telnet
I hope that helps
