a stencil mask problem that took me over 20hr for no answer...

hi everyone, I was learning to create a Field Of View from a master's instructional video on youtube link text, I followed a series of his teachings and modified it to a 2D version, and here comes the problem: my stencil mask shader works fine on other objects, but it just doesn't work on the FOV mesh.

I've tried the following myself but none of them work: 1. Replacing 2D objects with 3D objects (sprite to mesh) 2. Rebuild on three versions: 2017.4.11f1, 2020.3.19f1, 2021.2.10f1 3. Avoiding Stencil may be abnormal in LateUpdate

I think that the biggest possibility is the problem of mesh rebuilding at runtime, but I can't find any relevant answers at all.

I really tried my best to find the answer, but it all came to no avail, please help me to overcome this problem, my sincere thanks!