Google's John Mueller reminded us on Twitter that manual actions still do expire, we knew this from 2011. He also added that sometimes when they expire, they might not come back as a manual action because an algorithm might deal with it in the future.
Again, almost all SEOs know that manual actions can expire, we reminded you of it in 2011 and 2013. In fact, most SEOs with penalty experience have seen this first hand.
John added that sometimes if a manual action expires and the webmaster doesn't do anything to fix the issue that it might mean that an algorithm is dealing with it now and human manual actions are no longer needed. So if you have a link manual action and you don't clean up those links and the manual action disappears after a couple of years, it might mean that maybe Penguin is dealing with it.
John wrote "Yes, manual actions expire after time. Often things change over the years, so what might have required manual intervention to solve / improve back then, might be handled better algorithmically nowadays."
Here is the context:
Yes, manual actions expire after time. Often things change over the years, so what might have required manual intervention to solve / improve back then, might be handled better algorithmically nowadays.
— John ☆.o(≧▽≦)o.☆ (@JohnMu) September 7, 2018
Forum discussion at Twitter.