Era beginning/end
The seasonal Fae Courts split from the Material Plane and move their lands into another pocket dimension/plane.
The seasonal Fae Courts split from the Material Plane and moved their lands into another pocket dimension/plane. In order to keep the world's land from shifting like when the Celestial Fae Court completely disconnected their land from the globe and into another plane, they kept many small gates and portals between their planes and the Material Plane. This is why the courts still technically appear on the world map, since their lands still "exist" on both planes, yet a person can't simply pass from one to the other without entering a gate or portal. When this Schism happened, a strange glitch in space-time occurred. Instead of entire portions of land being moved, an entire group of Fae were displaced and transported to the Material Plane, while non-Fae peoples replaced them in their Fae Courts. This is how an entire group of people completely disappeared from the land that was renamed Sylvia, and their descendants are Fae/of Fae ancestry. Meanwhile, the people who once lived in Sylvia now live in the Spring Fae Court. This shattered much trust between the Spring Fae and their neighboring courts who had not listened to their concerns, as well as the average Spring Fae and their government. The Spring Fae Court began to isolate themselves even from the other Fae Court for centuries after this occurred. The seasonal courts have not cared to leave their planes or help those who were replaced and left behind on the Material Plane. In fact, the two haven't been able to communicate easily with each other due to the distance and planes between them.