Tried looking up "cdn.sstatic.net" on meta but found nothing recent. Whenever SO is slow to show up in the browser, it's because it's stuck waiting for "cdn.sstatic.net". Also in the most extreme slowliness cases (might not be related) every once in a while the site shows up apparently without any CSS styling on my smartphone (running Android 4.1.2, that never happened on my desktop computer).
There is a similar meta question here, but it's from 2011 (with comments from last year saying it's still relevant) and if it's any use, I'm in eastern Canada (Québec).
Is it a known issue? - this year I mean.