CM1200/CM2000, Asus RT-AX86U, & Comcast 1.2Gb internet

Final Update: So in the very end, I believe this was not a modem, router, cable line or any device issue. This was an issue of not being provisioned right and messing with the main cable line tap, was the reason why I got my full provisioned speed - something along those lines. Now with my CM1200 with LAGG enabled, to my RT-AX86u with LAGG enabled, I am getting 1200+mbps to all my connected devices. Using the 2.5g output port on the router into my desktop pc with an Asus PCE2500 ethernet card I am seeing fantastic results.

So, if you have these 2 devices you can at least save yourself money and don't need to upgrade your modem to access higher than gigabit speeds even when comcast says the CM1200 doesn't support more than gigabit speeds. Thanks for everyone elses help across many different forums and calls.

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Issue: I've got comcast 1.2GB speed, provisioned 1400Mbps and I want to take full advantage of what is paid for. Currently getting 940mbps across all devices.

Equipment:
New CM1200/CM2000 modem.
New Asus RT-AX86U router.
New Cat6a patch cables.

Sketchy cable line with tight connections.

Question: How can I get this to work or is it already working?

Method/Results: I've got Ethernet Port Aggregation turned on the CM1200 and have 2 cat6a cables going into my Asus router from its 1 & 2 ports... The router has WAN aggregation turned on and instructs to plug the cables into the 1Gb wan port and Lan port 4. At this point, the router should be receiving full signal and spread 1200mbps across all devices connected, but it still topped out at 940mbps.

The above wasn't working so I bought a CM2000 and connected the 2.5g into the 2.5g port on the asus rt-ax86u turned off any aggregation and still did not get provisioned speed.

I spoke with 4 comcast reps who all confirmed I was receiving the correct signal.

Notes: In order for my devices such as my PC to get 1200mbps since it does not have a native 2.5g port, I would need to either buy a 2.5g+ network card with lan aggregation which is super expensive and bond lans 1&2 on the rt-ax86u and the card to get that speed, or I can use wan aggregation across the CM1200 to the Rt-AX86u and use the routers 2.5g lan out a cheap 2.5g network card on my computer and get provisioned speed... saving $$$$. Wifi is ignored.

I can confirm it was a bad cable line. My own wire was run from the tap and I am now getting 1300mbps+ with the CM2000 & RT-AX86u. Check your cable lines. I will retest with the CM1200 with aggregation enabled and update!

Update: I had the old cable line hooked back up and plugged the CM1200 back in, reactivated, and now I am getting 1300+mbps over aggregation between the RT-AX86u and the CM1200 across multiple devices, totaled. This process has been insanely frustrating for me but I have learned a lot but ended up doing nothing. At this point in my conclusion, it seemed like "unplugging the cable line & plugging it back in" worked, (for whatever reason that may have sent a new provision from 940mbps to 1200mbps, all ethernet cables kept the same, so I'm not sure if any/what variable actually changed, connections were super tight before, all reps said I was receiving the correct strong signal the entire time, maybe nothing happened), moving on, I'll be returning the CM2000.  I'll update once again when I get my network card for my PC and can access all 1200mbps+ from one device and see if everything is working properly that way.