Wuxia authors sometimes go out on tangents from which they almost don't come back to the main story. These often have the effect of grinding the momentum of the story to a halt. Some infamous ones:
LOCH: The whole Ying Goo/South Emperor/Chow Bak Tung affair really ground the momentum of what had been a very exciting series of events in the lives of young Gwok Jing and Wong Yung to a halt. The story recovered soon enough, but it was an odd (and somewhat dull) detour.
ROCH: Passionless Valley. 'Nuff said.
HSDS: The whole thing with the Persians, while actually sort of interesting, also sort of stalled the momentum of the main story.
Any others?