Xfinity Speed Throttling

I have been a customer of Xfinity/Comcast for almost 3 years since I bought my first house. Starting in March, I noticed that my internet speeds were not reaching my paid for speeds of 800Mbps Download and 25Mbps upload, but instead I was getting 80-90Mbps download and 25Mbps upload. I restarted my modem (Arris Surfboard SB8200) and the issue seemed to resolve itself for a few days and then the issue reappeared. I contacted Xfinity Support and their only suggestion to me was that my modem was bad and I needed to replace it. So I went to Best Buy and bought a brand new modem of the same exact model and installed it and my speeds were restored.

This issue didn't reappear for the next several months until the end of August when it happened again. This time, restarting the modem didn't even help restore my speeds. So I got in contact with Xfinity again and they scheduled to have a technician come out and check out everything from the tap at the street to the modem. Ultimately, after all of his diagnosis, he determined that my service line from their tap at the road was bad and he ran a temporary cable and also installed a signal amplifier to get everything within spec. After that, my speeds were restored and everything was running smoothly. This all happened yesterday (9/6/23) between 8-10AM.

After he left, I went to work and got home afterwards and everything was till working as it should. My girlfriend works from home for a hospital and she said she didn't have any issues after he left so I thought that finally my issues were resolved once and for all.

Or so I thought.

At about 11PM last night, I get another notification that my internet had been restored after a brief outage. Out of curiosity, I ran a new speed test. And guess what? My speeds were once again throttled down to 80-90Mbps download and 25Mbps upload!

Has anyone else dealt with issues like this and if so, how did you ultimately get them resolved? This is getting exceedingly frustrating and it makes me want to cancel all of my Xfinity services and just switch to something like T-Mobile home internet or Starlink since there is no other hardwired ISP options where I live.

For reference, my networking equipment is all business-grade Ubiquiti equipment. That includes a Unifi Dream Machine Pro, PoE Switch, and 2 WiFi 6 access points.