Spectrum 400mb down Internet subscription, but only getting about 200-280mb down on router.

Hello, 

I purchased a Netgear AX-1800 (Model RAX10-100NAS) 3 weeks ago as an upgrade for my Asus AC1200. When it was first installed I had no problem hitting 450mb down when I first installed the new router.

After a few weeks of use, my speeds dropped from 450mb to 200-280mb down. Haven't done anything with the QoS or with the Access controls.

When plugged directly into the Modem (Spectrums newest Ubee modem) that was provided by my ISP, I can achieve 400mb no problem, but once it's connected to my new router setup, speeds drop to 200-280mb. It randomly spiked up to 450mb one day and only maintained that speed for about 2 hours and dropped back to 200-280mb. That was 12/11/20. Firmware verison is V1.0.1.80

All of the test have been ran through a PC that is wired directly to the router. I have made sure my ISP provisioned my household for their 400mb subscription.

ISP has already sent out tech to change the line out, changed all the connectors, Modem has been replaced twice, and all CAT5e wires have been replaced. Factory reset my router already, still the same speeds.

Anyone have any other suggestions?