What happens to the surface?

How to fix the problem?https://aws1.discourse-cdn.com/mcneel/uploads/default/original/3X/d/5/d59b05cdca00c12b3eda6f3e68bb362304907b88.mp4

Probably a bad trim. Does “Check” show any issues? Generally the solution is to Untrim the surface and re-trim cleanly.