@Djaggs You might enable the Private Address on those phones, check this link for more details.

@jchaves2m How did you observe the fixed channel still changing automatically? Which channel you were trying to fix on the AX6000, and which channel does it switch to? Are there range extenders...

@BJohn I believe you are referring to QoS, but not DOS. That's a good try.

@japaul32 That's bad. So are both the 2.4G and 5G networks dropping the connection? Are you enabling the Smart Connect feature on the AX73? What if you try disabling it? I saw some threads mentioned...

@ETG312 Even though they are both AX1800 series, they are different models and hardware versions, you cannot upgrade or install the firmware for AX1800. Just like Kevin suggested, it would be better...

@japaul32 Seems similar issue as reported by airchaser here, and TP-Link suggests changing the wireless security to WPA2-PSK[AES] for the 2.4G network.