Legacy edge detection image effect + post processing not working

Hi everybody,
I have a few effects from the new post processing stack in place and I later decided to add an edge detection effect to add a toon-ish outline. For this I’m using the legacy edge detection script. Both the edge detection and post processing work separately, but whenever I enable the post processing stack the edge detection script stops working. This appears not to be related to the effects I have enabled in the stack, as the problem stays even if I disable all the effects in the stack.

A few images to illustrate my problem:

Only legacy edge detection script

Edge detection + post processing stack

What am I missing?

Thank you for your help!

I have not this problem but you can try this: