@Matrp 

The same thing happened to me

@Tavocampana did you figure it out ?

@Matrp 

No, it happened to me yesterday and it is the first time it has happened to me. I did a hard reset to get back to normal.

Anyone has an idea why this problem occurs.

I know we should put devices on UPS, but this behavior is not normal, UPS or not.

I've heard of a router configuration file being defaulted due to a sudden power outage, but not just wireless being deselected from the config menu. 

I would also recommend placing the router on a backup UPS, if the router keeps experiencing power outages it may damage it.

@Tony 

I absolutely understand and agree that UPS is as great way to prevent power failure. Nevertheless, it doesn't explain the repetitive lost of wireless configuration.

@Matrp 

You could try reflashing the latest firmware it already has to see if the current configuration file may be the issue. Settings should be saved in the router so if you physically pull the power or turn it off or get a power surge all settings should come back. If you tried reloading the firmware, and can still replicate the issue or the problem still happens there may be an issue with the router.

@Matrp 

After factory reset and update, I cut the power to the router (breaker shutoff). Sadly, the problem persisted any idea ?