Solved! Solved: Go to Solution.
Someone asked a similar question about authentication that keeps reverting to default every time they restart their modem and they were also using a Sagemcom 5366. I am wondering if this is the same issue where a separate page somewhere in the admin actually saves any changes that have been made.
I did not see any mention of a reset in your first post only that when you turn it off and on it loses the settings. If you actually do a reset it will lose those settings.
Old versions of the firmware have been reported to have the problem of loosing setting after being turned off.
The GOOD news.
In the spirit of trying absolutely everything, I restarted the modem via the My gateway app (there's an option on the maintenance tab). Before that I'd been using the power switch, and that was doing a factory reset, losing all previous settings
The latest firmware version is SG4Y1T000085 which does not appear to have that problem. See above quote for possible way to force firmware to get updated.
No it should not lose those settings when you turn it of and on. Have a good look around the admin interface possibly under management. Not sure if the admin has a basic and advanced screen so you might want to look at that as well. As I said in the other post I might be barking up the wrong tree but some modems do have a save and reboot function to keep any custom changes.
Yep firmware issues as YetAnotherAcc advised can also cause issues. I did see a reboot option under management in a different model so I'm not sure if that one has it as well.