@Shishi22 Reset the RE215 to its factory defaults by press and hold the reset button for about 10 seconds. Once reset use this video guide to connect RE215 to your ISP modem. Using an ethernet cable...

@Hizzzon AX12 is a dual band wireless router: IEEE 802.11ax/ac/n/a 5 GHz IEEE 802.11n/b/g 2.4 GHz It can provide dual band wireless connectivity in both wireless router mode and access point mode.

@TheFriendly Test the speed from a wired device and make sure that QoS feature is disabled:

@Rich---- I understand your point regarding different proprietary mesh technologies. Many network equipment manufacturers have developed their proprietary mesh technology as well. AFAIK what TP-Link...

@MarcoDzz That's not the way that REs work - see more details in this thread.

@Barra8 If you change the modem then it's better to reset your RE650 and re-configre it from scratch. To reset the RE press the reset button for about 10 seconds.