https://en.wikipedia.org/w/index.php?diff=prev&oldid=950602405
The bot tagged a fully working URL as dead, due to it having {{full|date=May 2018}} next to it, causing the bot to check if http://www.physics.ohio-state.edu/~kagan/phy367/Lectures/P367_lec_14.html%7B%7Bfull%7Cdate%3DMay was dead instead of the actual URL http://www.physics.ohio-state.edu/~kagan/phy367/Lectures/P367_lec_14.html (please note the extra %7B%7Bfull%7Cdate%3DMay in the URL)