I don't know if it's a real thing, but it's what I call it. Jordan wrote 3 pretty solid books to start his series, and the third had a sort of plateau ending. Not everything was resolved, but several main characters had a satisfactory arc come to some sort of closure. The story could go on, but it would be a new age/era for most characters. I felt much the same about ASoS.
Cue book 4, where those threads are dropped to focus on some entirely new conflict complete with entirely new civilizations. Jordan dropped his cosmic conflict to start telling stories of political horse trading among the aes sedai, seanchen, and desert people. He spent the next 8 books writing unending soap operas about these political squabbles before dying with the series unfinished. They had to bring in someone else to write 3 MORE books tying up his loose ends and finally delivering an epic final battle.
Cue GRRM who after book 3 hit a wall and after years only managed to turn out a book 4 focusing on the political scheme's of b-characters. We abandon the Stark's and Lannisters and dragons and other contenders for the throne to instead learn about internal dynastic drama among the sea people, desert people and maesters, all while Breanne goes nowhere to accomplish nothing. By all accounts, book 5 brought things scarcely closer to any conclusions.
It's my shorthand term for when an author has an exciting and engaging start, but has no idea how to end the story and no editor to stop them from chasing down every side plot to avoid/stall the ending.
It applies to Patrick rothfuss as well. No way does he wrap up the kingkiller "trilogy" in the third book.