See report at https://www.mediawiki.org/wiki/Topic:Twpg9elwi18x98m6
which includes a URL fragment that begins with /w/api.php?action=query&format=json&prop=info%7Cpageprops%7Cpageimages%7Cpageterms&pithumbsize=80&pilimit=50&wbptterms=description&ppprop=disambiguation&titles=1912 and ends with &continue= Failed to load resource: net::ERR_CONNECTION_CLOSED
The reporter normally edts at the Russian Wikipedia.
The first bit of their copy-paste appears to be irrelevant to this issue, as it's just a query to get some page properties, probably for the link inspector.
The relevant bit is "Failed to load resource: net::ERR_CONNECTION_CLOSED" which implies connection issues. Either their internet died, or the request was blocked by their ISP, or blocked by us, or blocked by their browser, or... well, any number of things. There's no way we can diagnose this, and even if we could, I suspect it's not a problem we could fix anyway.
In the absence of any more information, there's nothing to do here.
The editing environment could handle this random problem more gracefully, though. I will file a task for that.
The original reporter was using Chrome on Windows 7.
Article: https://ru.wikipedia.org/wiki/Российский_университет_кооперации
The original reporter says that this happens intermittently, which suggests a problem with an internet connection (and not, e.g., malformed wikitext on the page).