AR Portal stencil shader jitter issue

Hello everyone , i am working on AR portal using Stencil Enable disable function using shader ,

all working good as aspected but while entering and exit shader value change make glitch in render. any one has solution for this problem?

or any other way to make AR Portal ? i had already try masking but its worthless in my case.


for better understand my issue look this tutorial

 

I have the same problem, do you found a fix?