Extreme slow speed for for servers in certian states (east and west coasts)

I have a very similar issue like from this post. https://forums.xfinity.com/conversations/your-home-network/certain-websites-and-apps-loading-content-super-slow/678622f182448c7bf166a3b2
Since a few days ago, I've noticed some websites or services are much slower or even unusable. For example, I could get 4k streaming smoothly from PrimeVideo but can't even load DisneyPlus's app.

I tested it today with Comcast's own speedtest website and confirmed my concern, while I can get around 900Mbps from several servers in a few states, for a few other states I could barely get up to 2Mbps. I've restarted the cable modem and all signal readings are strong (thus the 900Mbps result). I also noticed around 15 ~ 20 % packets lost when pinging a VPS hosted in a California DC.