The original lunar landing hoax hoax was preached by the founder of the 20th century version of the Flat Earth Society (born in UK, but living in the USA at the time). Since you cannot orbit a flat Earth, the entire space program was fake (according to him), including the lunar landings. When he died, that hoax went dormant.
The resurection of the lunar landing hoax hoax was popularized by Bart Sibrel (a "journalist"). Tired of not being believed by the majority, Bart devised a "sure" scheme. He would get an astronaut to swear on a Bible that he went to the Moon, then sue him for perjury.
When he did try his scheme, Bart ended up getting punched in the mouth (deservedly) by Buzz Aldrin. Then Bart got laughed out of court.
Lately, this (and many other) hoax has been restoked by those who publish fake news via Twitter, Facebook and other medias. The purpose is to destabilize people's confidence in their government, agencies and people of authority.
PS: Nibiru is totally different. It is a fictitious planet created for a fiction story (The Twelfth Planet, by Z. Sitchin, around 1970). In the story it never hits us, it never even hurts us. In the story, it cannot come near us before the year 2085.
There is a fake planet X (a rogue planet) popularized by Nancy Leider, for the end-of-the-world hoax of May 2003.
For the Big 2012 Hoax (the so-called Mayan Calendar end-of-the-world), the hoaxers combined Planet X with Nibiru (and even throwing in Nemesis); it is this combo that keeps destroying Earth almost every year since 2012. Not the original Nibiru.
The lunar landing hoax hoax is NOT from the same people that brought us any of the three versions of Nibiru.