[copypaper]

I've had it happen to me exactly once in the past few years. And a simple refresh fixed it. Definitely an overstatement to say it's common.

[userbinator]

Somewhat common if a site is being overloaded.

[saghm]

That checks out, I feel like the place I've seen it the most is on Github, which also seems to be the site I use regularly that has the most frequent outages (which also aren't quite at the level I'd call them common, but still _somewhat_ common_ compared to everything else I use anywhere close to daily)