@RyanEverhart789 I'm having EXACTLY the same problem even down to using AT&T and the speed (around 530 MBits). Was hoping this problem was solved on the forum

@mnrbradley lets work on this one together! 

@RyanEverhart789 

The speed test in the Deco has not been accurate in the past. If you want to perform a speed test use a wired computer to the Deco and use a speed testing site or speed testing app on your smartphone. If all three are showing the same speeds then that will show a lower speed is happening.

@RyanEverhart789

Just out of curiosity, have you tried plugging your M9 directly into the AT&T router? That's how mine is set up - it's not going to a switch first. I wouldn't expect that to make a difference, but it would at least verify that it's not a problem with the switch.

The other thing that I did on mine is to set the AT&T router up so that my M9 is in bridge mode (or IP Pass-through). I'm trying to treat the AT&T router as nothing more than a cable modem and my M9 to be my main home router. I followed the steps in this forum to make those changes (except I didn't need to change the Arris subnet because it's already on a different subnet than the Deco's default)

https://www.reddit.com/r/Ubiquiti/comments/b1x5l6/how_to_properly_configure_the_arris_bgw210_for/

Unfortunately doing this had zero impact on the speed test within my Deco M9+ (v2). I just did the recommendation of connecting a computer up directly to the Deco M9 and doing a speed test and it also gets the slower speeds (even a little less than the M9 does). So then I hooked a computer up directly to the AT&T Router (Arris) and that computer ALSO got slower speeds.

I think this narrows it down for me. Something is wrong with the AT&T router and it is not sending through the full speed on the cables. The color of the connection is green indicating a Gigabit connection (orange would indicate a 100MBit connection). I also tried changing the connection type from Auto to Full Duplex Gigabit but that didn't change anything. I guess I have a call to AT&T in my future.