I have learned that "in the weekend" is a kind of weird expression, and that we should use "on the weekend" or "at the weekend" instead.
I, however, noticed that the phrase can be seen sometimes even on prestigious newspapers and magazines as in the below examples, and I just would like to confirm with you whether they are all errors or not. I'm curious if there's any exceptions.
The Guardian
"I don't know if I'll be here next season". His comments came before his opposite manager on Saturday, Chris Hughton, was sacked later in the weekend.
Financial Times
Although senior executives might not have been rushing to the office in the weekend, most banks’ analysts were.......
The New York Times
In Asia, where trading ended before Monday’s de-escalation, markets suffered steep losses, reflecting the trade turbulence earlier in the weekend.
Time Magazine
The fifth winter storm of the season is forecast to move from the Mississippi and Ohio Valleys on Friday before pushing to the northeast and into New England later in the weekend.
POST EDIT (I added some more examples)
BBC
The election committee gave no date for a declaring the result, but the speculation is that it might be announced in the weekend.
Nature
the total distance of taxis has a low peak in the afternoon of the working days, but not in the weekend; the total distance of buses has two peaks in the morning of workdays but only one peak in the weekend.
Forbes
In the weekend of their first launch, Hoyt and Yanda made $120,000 in course sales.
Sydney Morning Herald
And so it was in the weekend, when a reporter was rude enough to ask US Environmental Protection Agency chief Scott Pruitt about the impact of climate change on monster hurricanes that have been smashing southern states, he responded:
