Greek Fire was a potent technology that could essentially act as medieval napalm, Easily burning enemy ships to nothingness causing massive damage to entire fleets.
And yet, today, the recipe to make Greek Fire, developed by the highly bureaucratic Byzantine Empire who no doubt kept their records, is lost.
History would suggest that any technology, no matter how powerful, is not invincible to being lost. And when no crewed missions to the moon are made in 50 years, it's entirely possible that the old, archaic computers storing scientific data broke down, old notebooks were destroyed in a storm, or the scientists who devised the ahead-of-their-time technologies had passed away.