CPL is not working in a room anymore.

Thank you for your complete response. I've tried all the outlets in my room (without a power strip), and each time it's the same: only the powerline adapter light doesn't turn on. I've unplugged everything, but nothing changes.
No new electrical devices have been plugged in the house for a week.

As you told me that it works in another room, we need to think like this: the PLC operates through the electrical network, which is composed of different circuits that connect to the same panel (the one with the fuses).

If there is a disturbing element, it will pollute the entire segment coming from the panel.

So if the circuit/segment serving the room also serves other rooms/places, it’s the entire circuit that needs to be checked, not just that room.

For example, I had a monitor’s power supply that was starting to "fail," so nothing perceivable from the outside, but I regularly lost the entire PLC because my main box was on the same circuit. I eventually found the cause partly because the monitor had a slight burnt smell, but you had to get pretty close to it.
Once it was unplugged, zero problems.