Yoast founder Joost de Valk has issued an apology over a bug in the company’s WordPress plugin that caused some websites’ search rankings to drop.

Earlier this week, de Valk wrote a blog post detailing what a bug found in Yoast SEO 7.0 did to certain websites. The bug basically set the attachment URLs to “no,” which shouldn’t be the case. Attachment URLs are important because websites actively link to these pages, which contain real content.

If the setting of attachment URLs is set to “no,” the site’s ranking is affected because Google would notice a marked increase in the number of superfluous URLs generated by the WordPress website. Fortunately, the bug has now been fixed.

“The bug was simply yet very painful: when you updated from an earlier version of Yoast SEO to Yoast SEO 7.0–7.2 (specifically those versions), we would not always correctly convert the setting you had for the old setting into the new one. We accidentally set the setting to ‘no.’ Because we overwrote the old settings during the update, we could not revert this bug later on,” de Valk explained.

The founder maintained that only a few sites running the WordPress plugin suffered due to the issue. However, he deeply apologized because of what happened. “The vast majority of the websites running Yoast SEO probably hasn’t suffered at all. Still, we messed up. I myself, am sorry. More so than normal,  because I came up with and coded this change myself.”

Meanwhile, some plugin users whose sites were affected by the bug voiced out their disappointment online. “My site has completely disappeared from Google. I was ranking 2nd or 3rd position for lots of terms, and it just disappeared. This is a serious bug, and something that has affected me … I have lost confidence in your company and plugin forever,” one wrote.

“Honestly, this issue cost me a lot of money. I run a content website that heavily focuses on photos, and my site traffic plummeted to less than a quarter of my normal pageviews as a result. I easily lost $1-2k this month. Really disappointing, but glad that it’s been fixed,” Jessica Bishop, the creator of The Budget Savvy Bride, stated.

Though the bug does not affect everyone, Yoast SEO users are advised to check on their plugin settings if they noticed a drop in their search rankings and traffic in the last three months. Update 7.0 was launched on March 6, so users who noticed dramatic changes to their online visibility ever since the update arrived should now have a clue what went wrong.