Simply put I have Xfinity 1.2 gig service with a not even year old S33 modem.  When I plug my Chromebook via gigabit Ethernet adapter into the 2.5 or 1 gig port I get around 500-600 mbps down.  Xfinity tech comes out & connects his meter to the incoming cable & showed me it was getting 1.299 gig.  Then he plugged his meter into the cable coming out of the 2.5 gig port and it also showed 1.299 gig down.  That’s the first issue, now the rest of it that makes no sense to me;

I have a band new Amplfi Alien router w/ the LCD touch screen.  It shows Xfinity’s speed coming into the router usually between 750-810 mbps but when I plug my Chromebook into one of its LAN ports I get 570 mbps down which I don’t understand.  Then here’s the last piece that makes me even more perplexed;

I have a TP-Link RE650 gigabit range extender (which is connected via wifi to the Alien router) and when I plug my Chromebook into the LAN port on the range extender I get speeds of 720-800 mbps down.

So at it’s simplest; I get 500-600 mbps when connected via Ethernet to the S33 even though the tech showed me the 1.299 gig signal going in & out of the S33.  Why am I not getting true gigabit speeds?  I brought my Chromebook over to my brothers house and plugged into his modem and got 1.1 gig, so I know it’s not my Chromebook that is limited (plus I get 800 mbps when connected to the LAN port on my range extender. 

Any help from the experts here is greatly appreciated.

EDIT: I just did a speed test with my iPhone 12 & got 822.8 mbps down.  So LAN gets 500-600 & on my phone I get over 820 mbps which is odd.