@JackD Is the problem with these two devices only or with every device you use ? If you don't have Auto then try setting WPA-PSK / AES just for the test. I suppose the wireless signal is strong...

@PauliMoon There could be a strong wireless interference around you on 2.4GHz band - you can check that with: https://www.metageek.com/products/inssider/ or Wi-Fy Analyzer. If that's the case you can...

@JackD It seems that there's a newer FW release for your modem here. You could try to upgrade to the latest one and test again. If the issue persists forget the wireless SSID from your mobile and...

@Saintjp Actually the warning about WDS incompatibility is published in one of the the official guides for using WDS feature. When you open the link (blue text) look for the text in red to read the...

@vasik006 Check your FW region on the router bottom sticker. The beta in question is for C6 v2 EU region. On your original issue - try forgetting the wireless networks on your mobiles and re-add them...

@john_smith49 That's not easy to troubleshoot - probably a HW issue. If the device is under waramnty just contact your local support and ask them to be advised on this.