@Ivaylo Is it possible that the problem was that i use the same SSID for the 2.4 ghz and 5 ghz band?

@Ivaylo The router ping well all the devices. Yes the devices are in the ARP list AND in the DHCP client list. Now i forced my phone to the 5Ghz band (putting in the MAC filtering on the 2.4Ghz...

@Ivaylo I selected WPA2 but nothing changed. In my firmeware (european) I can't select the region.

@Ivaylo WPA version is setted to auto. Should I change to wpa2? The rest is already like you posted. I can't find where to select country.

@Ivaylo I always had some issue to connect to some devices. Now I realized that it depends on the band. I updated the firmware but the problem seems the same.

@Ivaylo the signal is strong. The device is well connected to internet. It just don't see devices on the other band. But it connect well with wired devices (NAS, and others...)