Shortly after the xkcd PHPbb forums were confirmed as hacked on 1 September 2019, all web services hosted on their server - including the original Geohashing wiki - were taken offline as a precaution. It took until 2 February 2020 for the wiki to be restored at its new home of geohashing.site.
The period between these two dates, when geohashers were unable to access the site, is known as the Dark Ages. It didn't stop enterprising explorers from setting out on expeditions, though.
A Dark Ages achievement for these brave souls* is available.