That's a connectivity issue on your end

. (I mean, the main OTA server was down for a few days around the 25th, but that's no longer the case; and none of the mirrors were affected).
EDIT for clarification: the following applies to people experiencing that *right after a connection*, but for whom a retry or two fixes it.
(If your AP or router is a bit sluggish, the first few seconds of connectivity can be a fair bit spotty; this seems especially prevalent on Kobos. I've barely seen it happen since revamping my wireless network, FWIW).