Network issues | High ping/latency/packet loss

I’ve been having issues with high ping/latency/packet loss for several weeks now affecting my ability to game online. I’ve actually been banned/restricted from playing against other players online due to an “ongoing network issue negatively affecting the gameplay experience for others”. It’s easiest to see the ping spikes during speed tests, where I can see that the ping spikes when downloading or uploading data. Otherwise the ping sits relatively low. Previously the ping was shooting up to around 800+ms, but now the highest I’ve seen it go is around 600ms.
I’ve tried everything at this point including upgrading my speeds, getting a new gateway, trying wired/wireless connections, putting the gateway in bridge mode and using a high-quality gaming router, power-cycling the modem and router, swapping out the coax and Ethernet cables, etc.

I initially reached out to support through the Xfinity Assistant; the first agent tried to upsell me to a faster plan as a solution until I requested someone with an actual understanding of technical issues. The second agent seemingly knew a bit more and stated they had detected an issues with the lines running from the street to the building and scheduled a technician to come out several days later. When the technician arrived he informed me that he had received no information about any issues with the lies and that the agent had completely made that up. The technician ran some tests on the gateway and said there were issues with it, so he swapped out the gateway. Afterwards the technician stated it was functioning properly and the speeds were coming through consistently, but he had no idea what was causing the ping/latency and it has not been fixed. I’m not sure if these issues are from some sort of signal degradation, issues with infrastructure hardware in the neighborhood, or something else. I’ll attach some images, please let me know if there’s any other info I can provide. 

https://imgur.com/a/cdt4ZsI