Has it always had this behaviour?
Have you tried restoring the default config or doing a factory reset.
I would guess that previous use of this command has broken something. Does anything show in the logs?
Yeah, it still does this after a factory reset.
I will try to wait for 30 minutes and see if the internet LED will ever turn to green without issuing an "adsl configure --snr xx" command.
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EDIT: Well ,it still behaves like this and it's unnacceptable but I found a solution which may be considered a workaround, because not anyone can do this (unless they own a server, a NAS or other small device like router or AP with linux , working nearly 24/7 on their local network).
I have created a watchdog script on my linux headless server that sends this exact adsl command to the router every 2 minutes, succesfully restoring the internet, only if it (the server) can't ping 8.8.8.8.