A lot of these notes have been outdated by the invention of Wikipedia, but I’ll present it anyways.
Fakelore is considered the cowpies of folklore, as they are new creations that are played off as traditional stories. They are especially common in the United States, where companies create promotional characters and play them off as traditional heroes. The primary example is the tall tale of Paul Bunyan, which some people consider to be an old folk tale but was actually a Disney creation of the 1960s. Many conceptions of Santa Claus are also American creations by the Coca Cola company. This may also refer to new definitions for old concepts, another problem that occurs in folklore with improving technology. For example, blue moons used to be quite literal but its definition has changed with astronomical developments to mean two full moons in the same month.
Folklorismus is the modern revival of formerly dead traditions, mostly from descriptions or recordings. Examples are especially common in Japan, which experienced an outburst of interest in traditions following decades of modernist rejection. Arts such as taiko drums or kimono dances were resurrected. Tourism is probably the most common reason for such a revival, as native entrepreneurs create or revive folklore to satisfy tourist demand.
The reason these are troublesome is that the origin is often obscured, making it difficult to distinguish between actual folklore and modern creations. This can complicate efforts to study social life in historical context. As a result, ordinary people often fill in their own blanks and create a new imagined origin. A good example of this is Rudolph the Red-Nosed Reindeer. People might give all kinds of answers if asked where the story came from. Interestingly, very few people know that the story was created by Robert May in 1939 as an advertisement for Montgomery Ward. (Protip: most Christmas stories are American creations)