Cannot Achieve Gig+ Wired Speeds After "Network Upgrades"

Hello,

Apologies ahead of time because this will be a very long post, please bear with me.  

Around the beginning of last year I was looking for a modem/router combo that would allow me to take full advantage of my 1.2 Gig Xfinity Internet service using a hardwired ethernet connection. 

I initially purchased the Arris S33 since it is advertised as having a 2.5 gig port.  I used this in combination with my ASUS RT-AX86U Wifi 6 router which also has a 2.5 gig port and 4 x 1Gig ports. 

I quickly realized that I would not be able to achieve WIRED Gig+ speeds with this combination.  Testing the S33 directly connected to my desktop computer of course gave me over 1 gig speeds.  But since the router I have only has the ONE 2.5 gig port (which can be used as a WAN port), I was unable to achieve over 1 gig hardwired speeds since the other ports only achieve up to 1 gig.

So the answer I thought?  Ok I will have to purchase a new router that has multiple 2.5 gig ports if I want to achieve wired Gig+ speeds...  but those can be EXTREMELY expensive.

After doing some research I discovered something called WAN Aggregation/Link Aggregation.  How cool is this!  You can use multiple connections from a single cable modem (when they generally only have one) to increase the data throughput to achieve over gigabit speeds.    

I ended up purchasing the Motorola MB8600 ->  https://www.motorola.com/us/mb8600/p

When I purchased this cable modem last year I did not see anything that suggested this modem was not supported by my current Xfinity internet plan.  It is advertised as achieving "up to 3.8 Gbps" Downstream.

My MB8600 + RT-AX86U router allowed me to easily achieve over gigabit hardwired speeds with WAN Aggregation enabled.  I would sometimes see as high as 1400 Mbps!  I was very happy that I decided to get this cable modem and did not need to purchase a new extremely high-end router that had multiple 2.5 Gig or faster ports.

My girlfriend and I moved to a new apartment last year at the end of May.  New location, same solid speeds.  I would still easily achieve over Gigabit hardwired speeds.

Around April of this year we received a notice from Xfinity that our area of town was "identified as needing network upgrades."  I thought great!  I would occasionally experience an unstable upstream connection so if anything I figured these "network upgrades" would make my connection ever more stable.

This is where things started to go wrong.

After these apparent "upgrades" to the network I was only able to achieve around 900 Mbps max speeds.  I realize "only 900" is a silly thing to say and being a bit extreme - but you have to realize that I have been paying for "Gig+" internet (and regularly achieved those speeds) before and now only on extremely rare occasions do I see it get close to 1 gig.  

I am fully aware that network congestion is a thing - but I have tried countless different speedtest websites (including the Xfinity speedtest tool) and at different times of the day when there shouldn't be many people using the network.  Same results.

I figured maybe there was some issue with the wiring to the apartment.  The building was apparently built in the 50s and the cable line into the apartment wasn't even from a jack - it was just a loose cable hanging from the wall... yet I was able to easily achieve the full 1.2 gig speed from my plan with my current equipment.

Moving forward to last month - we moved to a new place in the same area of town.  Building is a small house that was built in 2017.  Awesome!  Cable line should be solid and I might be able to experience my full speeds again.

Nope, same issue.  Using the same equipment (tested out multiple ethernet cables to my PC) and got the same results.  I would only achieve at best around 75% of the 1.2 Gig speeds I am paying for.  And I DO NOT use a VPN.

After multiple incredibly frustrating phone conversations with outsourced tech support representatives I was able to reach a "Level 2" advanced tech support rep based in the United States - PLEASE make that an easier process for people that know what they're talking about when it comes to more advanced tech issues.

She agreed that my issue didn't make sense since I have been using the SAME equipment for a year and a half now and regularly achieved the Gig+hardwired speeds before April of this year.  She also reiterated that using a hardwired connection should allow me to achieve the full speeds - I do not care about getting Gig+ WiFi.

She scheduled for a tech to arrive today to further inspect my issue.

Tech arrived today - have to give a shoutout to Don who works in the Davis/Sacramento CA area.  He was extremely pleasant and overall very helpful.

Don checked the signal coming in to the house and downstream was as high as 1600 Mbps!

Don mentioned that my cable modem is "no longer supported" for my current internet tier.  I was initially very confused why my modem used to allow me to achieve over a Gig hardwired, but after "upgrades to the network" would now only achieve around 900 Mbps.  I'm sorry but I do not understand how this makes any sense.  This modem is specifically designed to take advantage of multi-gigabit speeds.  Again the only reason why I decided on this specific modem was because it was stated as being supported for my current internet tier (at the time of purchase) and takes advantage of link aggregation.  WHY would Xfinity all of a sudden not support a modem for this tier that uses link aggregation?  The MB8600 is designed to be "future proof."

Don mentioned the my device info link through Xfinity.  There are about 10 devices shown which support my current internet tier.  And guess what?  NONE of the cable modems that are "supported" have link aggregation.  It DOES NOT MATTER if they have a 2.5 gig port (as described at the beginning of the post - this will not allow you to achieve Gig+ WIRED speeds).  

So I am stuck with a modem now that USED to give me Gig+ wired speeds, but now because of "network upgrades" I can no longer achieve those speeds??

Some help or suggestions would be greatly appreciated.  I would rather not spend several hundred more dollars on new equipment when my current equipment should be sufficient.