What exact link did you open? I don't find "latest log link" but assume you mean https://irc.geany.org/logs/current.php? Based on the issue create date(short after midnight UTC) and the fact that the link is working right now, I guess the logfile was already rotated but the new one not yet written to disk and so the file not found error occurred. The Supybot software buffers the logfile and only writes it every now and then to disk.
I guess I will make the script more robust to handle this case more gracefully.