Router does not maintain Wi-Fi channel

Sycret

WindTre-branded ex5601 router
I set Wi-Fi channels 1, 2, or 3... 2.4GHz
It lasts a day, then it always switches to channel 11.
The problem is that with the high channels, my Wi-Fi printer and video camera system no longer work (the devices connect at very low bitrates, the printer isn't even visible).
Why does it do this?
Until a few months ago, it was constantly on channel 3. Is it possible that a firmware update caused this?