Internet traffic levels (and the congestion that goes with it) ebbs and flows continuously. A path that my be clean today may be completely knackered up tomorrow. Weather patterns, major events that are getting streamed, new game releases (or major patches and expansions).... all kinds of things can impact things negatively at the drop of a hat. Many ISP's don't monitor things closely enough to catch them when they first crop up. Some only review routing metrics on a quarterly or semi-annual basis, so it's not uncommon for congestion spikes to go unnoticed for extended lengths of time. That is why it is important to verify our routes are not having problems. Even if SE's services were running perfectly, bad routing can still cause all these problems...and SE is powerless to address them much less correct them. That falls to our ISP's to investigate and affect repairs/upgrades/adjustments as needed.
Here is a map for my ISP's current outage reports and such. It gets archived periodically throughout the day, so it will update periodically and you may see the patterns change later. At present, the north east corridors are a mess, as well as several other areas.
Source: https://downdetector.com/status/time-warner-cable
You can see similar maps, statistics, and support posts for a long list of web services and ISP's at the main site:
https://downdetector.com/companies
Here's a couple other maps to review as well. You may notice patterns forming amongst them, because they all run into problems along the same routing points:
https://downdetector.com/status/att
https://downdetector.com/status/comcast-xfinity
https://downdetector.com/status/verizon-communications
https://downdetector.com/status/netflix
https://downdetector.com/status/playstation-network
https://downdetector.com/status/xbox-live
https://downdetector.com/status/call-of-duty