@Based_On_Cringe This sounds pretty much expected since the wireless connection has a half-duplex nature and on every hop it halves the bandwidth - 1'st hop (14 mbps) => 2nd hop (7 mbps). You'd get...

@Val1969 If you changed your main router then you should reset RE220 to its factory defaults (press reset button for about 10 seconds) and re-configure from scratch.

@Prash83 If your WA850RE is HW v7 (that's on its bottom sticker) update it to its latest FW version from here and test if there's an improvement.

@Tone42 There's no way to delay the router reboot time. If the router has an auto-reboot schedule feature you can use it to schedule a reboot (not sure if C9 has this implemented). In general if your...

@RockyBite If you connect them with a cable you can use them together (Deco in AP mode) but they won't build a mesh network. If you want a wireless connection between those two you'd better get an AX...

@JohnRose Try to delete that via Advanced=>Security=>IP & MAC Binding=>ARP List: or if that doesn't work just reboot teh router.