I would wager that this is due to a major cyberattack against the internet directory 'Dyn Managed DNS' which is knocking dozens of popular websites and services offline today, with outages continuing on and off throughout the afternoon.
So far sites such as Twitter, SoundCloud, Spotify, Shopify, Etsy, Reddit, and a bunch of other websites have been inaccessible for chunks of time to many users pretty much all day
The outages are the result of a distributed denial of service (DDoS) attack on the DNS provider Dyn. The company confirmed that as part of it's transparency policies and has a running update on the situation at https://www.dynstatus.com/incidents/nlr4yrr162t8
Dyn and other DNS providers operate as a link between the URLs you type into your browser and the corresponding IP addresses of where you re trying to contact. By attacking Dyn, it’s possible to overwhelm that directory function and cause outages and loading problems across a large portion of the internet.
So far it seems that most of the impact has been felt by users in the United States and since the company is actively trying to mitigate the issue the connectivity problems are coming and going and there's no telling how long it'll be lasting